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Effect of genotype and root colonization in biological control of fusarium wilts in pigeonpea and chickpea by Pseudomonas aeruginosa PNA1
Abstract
Pseudomonas aeruginosa PNA1, an isolate from chickpea rhizosphere in India, protected pigeonpea and chickpea plants from fusarium wilt disease, which is caused by Fusarium oxysporum f.sp. ciceris and Fusarium udum. Inoculation with strain PNA1 significantly reduced the incidence of fusarium wilt in pigeonpea and chickpea on both susceptible and moderately tolerant genotypes. However, strain PNA1 protected the plants from fusarium wilt until maturity only in moderately tolerant genotypes of pigeonpea and chickpea. Root colonization of pigeonpea and chickpea, which was measured using a lacZ-marked strain of PNA1, showed tenfold lower root colonization of susceptible genotypes than that of moderately tolerant genotypes, indicating that this plant-bacteria interaction could be important for disease suppression in this plant. Strain PNA1 produced two phenazine antibiotics, phenazine-1-carboxylic acid and oxychlororaphin, in vitro. Its Tn5 mutants (FM29 and FM13), which were deficient in phenazine production, caused a reduction or loss of wilt disease suppression in vivo. Hence, phenazine production by PNA1 also contributed to the biocontrol of fusarium wilt diseases in pigeonpea and chickpea.
... "Different mechanisms was reported for their performance such as production of antibiotics, siderphore cyanide hydrogen, competition for nutrition and space,inducing resistance, inactivation of pathogen enzymes and enhancement of root and plant development" [13]. "Pseudonas and Bacillus strain have great potential in control of Fusarium wilt disease of chickpea" [14,15,16,17]. "Plant growth promoting rhizobacteria (PGPR) have been reported as biocontrol agents of soil borne plant pathogen, offer an attractivelternative to chemical fertilizers, pesticides and supplements. ...
... However, for cultivar Burgeig, the ten isolates had a positive effect on severity, compared with the control, throughout the experiment except SA4 and SA6. Anjajah et al. [14] Hervas et al. [25] and Landa et al. [16] reported that Pseudomonas and Bacillus strain have great potential in control of Fusarium wilt disease of chickpea. ...
This experiment was conducted to evaluate the antagonistic effects of some selected rhizobacteria on Fusarium oxysporium f. sp. ciceris in a pot experiment. Rhizobacterial isolates (one isolate of Pseudomonas, eight isolates of Bacillus genera and one bacterium isolate) and two chickpea cultivars (Shendi and Burgeig) were arranged in a factorial pot experiment in CRD with four replicates. The disease incidence and severity were detected weekly. Disease reduction Original Research Article Abdalla et al.; Asian Plant Res. 26 percentage was estimated at the end of the study. Generally, the application of rhizobacterial isolates as biological control agent reduced disease incidence compared with the control in both cultivars. The incidence in cultivar Shendi occurred at the third week after inoculation when treated with Pseudomonas stutzeri strain W28 (SA3) and Bacillus subtilis strain CM14(SA9). For the two cultivars, Shendi and Burgeig, the Geobacillus sp. CRRI-HN-1(SA2) and Bacillus sp (SA1), respectively had the highest positive effect on disease incidence and severity throughout the experiment compared with the control. These were 45.36 and 44.82% in incidence; 55.36 and 63.89% in severity, respectively.
... Some opportunistic pathogens secrete diverse toxins that have antimicrobial activity against many other species of bacteria or fungi, making them strong competitors in host-associated environments (Tarkka et al. 2009;Hamad et al. 2020). Pseudomonas aeruginosa strains have the ability to outcompete other microorganisms, and can therefore readily colonize the plant rhizosphere or cause disease even in the face of potential competitors (Anjaiah et al. 2003;Spago et al. 2014;Yasmin et al. 2017). For example, P. aeruginosa PNA1 can produce two different phenazine antibiotics, phenazine-1-carboxylic acid and oxychloroaphin, which are required for PNA1-mediated protection of pigeonpea and chickpea plants against fusarium wilt (Anjaiah et al. 2003). ...
... Pseudomonas aeruginosa strains have the ability to outcompete other microorganisms, and can therefore readily colonize the plant rhizosphere or cause disease even in the face of potential competitors (Anjaiah et al. 2003;Spago et al. 2014;Yasmin et al. 2017). For example, P. aeruginosa PNA1 can produce two different phenazine antibiotics, phenazine-1-carboxylic acid and oxychloroaphin, which are required for PNA1-mediated protection of pigeonpea and chickpea plants against fusarium wilt (Anjaiah et al. 2003). Similarly, phenazine production is essential for microbe-microbe competition in acute and chronic P. aeruginosa infections in animals (Trejo-Hernández et al. 2014;Bisht et al. 2020). ...
Regardless of the outcome of symbiosis, whether it is pathogenic, mutualistic or commensal, bacteria must first colonize their hosts. Intriguingly, closely-related bacteria that colonize diverse hosts with diverse outcomes of symbiosis have conserved host-association or virulence factors. This review describes commonalities in the process of becoming host associated amongst bacteria with diverse lifestyles. Whether a pathogen, commensal or mutualist, bacteria must sense the presence of and migrate towards a host, compete for space and nutrients with other microbes, evade the host immune system, and change their physiology to enable long-term host association. We primarily focus on well-studied taxa, such as Pseudomonas, that associate with diverse model plant and animal hosts, with far-ranging symbiotic outcomes. Given the importance of opportunistic pathogens and chronic infections in both human health and agriculture, understanding the mechanisms that facilitate symbiotic relationships between bacteria and their hosts will help inform the development of disease treatments for both humans, and the plants we eat.
... aeruginosa); is a versatile bacterium found in a variety of aquatic and terrestrial habitats (Streeter and Katouli, 2016). Some strains are classified as rhizobacteria because they may colonize root surfaces and promote plant development (Anjaiah et al., 2003) whereas, other strains are capable of degrading environmental pollutants (Hasanuzzaman et al., 2004). It is also a notable opportunistic bacterium that may cause a range of diseases, including nosocomial infections (Del Barrio-Tofiñno et al., 2020). ...
... It is also a notable opportunistic bacterium that may cause a range of diseases, including nosocomial infections (Del Barrio-Tofiñno et al., 2020). Additionally, it has been reported as an effective agent in a variety of applications, including bio-control (Anjaiah et al., 2003) and bioremediation programs (Vieto et al., 2021). Moreover, it may produce several extracellular secondary metabolites, including pyocyanin pigment; this blue-green, water-soluble, nitrogencontaining, heterocyclic phenazin has enjoyed special interest due to its capacity to generate reactive oxygen species (Hassani et al., 2012). ...
... which are ubiquitous bacteria in agricultural soils, PGPR generally include the strains in the genera Serratia, cyanide hydrogen, competition for nutrition and space, inducing resistance, inactivation of pathogen enzymes and enhancement of root and plant development [9]. Pseudonas and Bacillus strain have great potential in control of Fusarium wilt disease of chickpea [10,11,12]. ...
... Kloepper [18] reported that Pseudomonas and Bacillus strains have great potential in the control of Fusarium wilt disease of chickpea. In addition, Bacterial biocontrol agents belonging to the genera Agrobacterium, Bacillus, Pseudomonas and Streptomyces, have been tested invitro and found to be effective against FOC in many studies [10,11,12]. ...
The use of chemical control causing negative effects non-target environmental impacts and development of pesticide resistance to applied agent, The great interest in eco-friendly and sustainable agriculture, push towards gradually shifting to biological control instead of dependence on chemical. The Fusarium wilt is biotic stress that constraint the production and expansion of chickpea crop in Sudan. The aim of this study was to use rhizobacteria as bio control agent against chickpea Fusarium wilt. Eighteen soil samples taken from chickpea rhizosphere collected from six locations in central and Northern Sudan (three samples from each location). The chickpea rhizospheric bacteria were recovered from the 18 soil samples and their antagonistic activity against the most virulent FOC isolate was evaluated in vitro (using 76 rhizobacterial isolates) and in planta (using the ten most potential rhizobacterial isolates). 31 out of 76 isolates (nominated as SA1, SA2…., SA31) were considered as virulent bacterial isolates, shown clear inhibition zones against the most virulent FOC isolate (FOCS9). The widest inhibition zone diameter (25 mm) was recorded for isolate SA1 (No. 1) and the lowest zones (13.0 and 13.7 mm) were recorded for isolates SA30 (No. 30) and SA31 (no. 31), respectively. Generally, the in planta application of rhizobacterial isolates as biological control agents reduced the disease incidence compared with the controls.
... Biological control is environment friendly and most accepted method used to control Fusarium oxysporum (Anjajah et al., 2003). Plant growth promoting rhizobacteria (PGPR) may be effectively exploited as control agents for the wilt pathogen (Schmidt et al., 2004). ...
... Wani et al., 2007 andVerma et al., 2014 reported that Bacillus, Pseudomonas, Trichoderma and Burkholderia show significant inhibition efficient bio-control agents for chickpea wilt. Trichoderma harzianum and Bacillus subtillis inhibit and suppress the disease by increasing β-1, 3-glucanase enzyme activity and ultimately suppressing the pathogen growth (Anjajah et al., 2003 andMoradi et al., 2012). ...
... Biological control is environment friendly and most accepted method used to control Fusarium oxysporum (Anjajah et al., 2003). Plant growth promoting rhizobacteria (PGPR) may be effectively exploited as control agents for the wilt pathogen (Schmidt et al., 2004). ...
... Wani et al., 2007 andVerma et al., 2014 reported that Bacillus, Pseudomonas, Trichoderma and Burkholderia show significant inhibition efficient bio-control agents for chickpea wilt. Trichoderma harzianum and Bacillus subtillis inhibit and suppress the disease by increasing β-1, 3-glucanase enzyme activity and ultimately suppressing the pathogen growth (Anjajah et al., 2003 andMoradi et al., 2012). ...
Fusarium wilt caused by Fusarium oxysporum f. sp. ciceris is one of the most important fungal diseases of chickpea limiting its productivity in almost all chickpea growing countries across the world. F. oxysporum is soil borne and root inhabiting in nature which may survives in soil for longer period (up to six years). Pathogen undergoes asexual reproduction by producing three types of spores; micro-conidia, macro-conidia and chlamydospores. Chlamydospores serve as primary inoculum for the disease occurrence. Prevalence and severity of disease are driven by inoculum populations and susceptibility of cultivar. F. oxysporum has high pathogenic variability having eight distinguished races and two known pathotypes. General symptoms of chickpea wilt are wilting, drooping, discoloration, yellowing, browning of xylem vessel and eventual collapse of whole plant. Delayed planting, seed dressing with fungicides, deep ploughing, use of bio-control agents and sowing of certified wilt resistant cultivars have been found helpful to minimize the disease prevalence. Through this review we have attempted to summarize the general aspects of fusarium wilt with an emphasis to pathogenicity and integrated disease management strategies.
... Moreover, soil applications of T. harzianum have been demonstrated to reduce the population of F. udum in the soil, consequently decreasing the occurrence of pigeonpea wilt 15 . Additionally, P. aeruginosa produces antibiotics like oxychlororaphin and phenazine-1-carboxylic acid, which have proven effective in reducing Fusarium wilt in both chickpea and pigeonpea 82 . Extracellular proteins from B. subtilis have been found to induce flocculation and vacuolation in F. udum mycelium 76 . ...
Fusarium wilt, caused by (Fusarium udum Butler), is a significant threat to pigeonpea crops worldwide, leading to substantial yield losses. Traditional approaches like fungicides and resistant cultivars are not practical due to the persistent and evolving nature of the pathogen. Therefore, native biocontrol agents are considered to be more sustainable solution, as they adapt well to local soil and climatic conditions. In this study, five isolates of F. udum infecting pigeonpea were isolated from various cultivars and characterized morphologically and molecularly. The isolate from the ICP 8858 cultivar displayed the highest virulence of 90%. Besides, 100 endophytic bacteria, 100 rhizosphere bacteria and three Trichoderma spp. were isolated and tested against F. udum isolated from ICP 8858 under in vitro conditions. Out of the 200 bacteria tested, nine showed highest inhibition, including Rb-4 (Bacillus sp.), Rb-11 (B. subtilis), Rb-14 (B. megaterium), Rb-18 (B. subtilis), Rb-19 (B. velezensis), Eb-8 (Bacillus sp.), Eb-11 (B. subtilis), Eb-13 (P. aeruginosa), and Eb-21 (P. aeruginosa). Similarly, Trichoderma spp. were identified as T. harzianum, T. asperellum and Trichoderma sp. Notably, Rb-18 (B. subtilis) and Eb-21 (P. aeruginosa) exhibited promising characteristics such as the production of hydrogen cyanide (HCN), cellulase, siderophores, ammonia and nutrient solubilization. Furthermore, treating pigeonpea seedlings with these beneficial microorganisms led to increased levels of key enzymes (POD, PPO, and PAL) associated with resistance to Fusarium wilt, compared to untreated controls. In field trials conducted for four seasons, the application of these potential biocontrol agents as seed treatments on the susceptible ICP2376 cultivar led to the lowest disease incidence. Specifically, treatments T2 (33.33) (P. aeruginosa) and T3 (35.41) (T. harzianium) exhibited the lowest disease incidence, followed by T6 (36.5) (Carbendizim), T1 (36.66) (B. subtilis), T4 (52.91) (T. asperellum) and T5 (53.33) (Trichoderma sp.). Results of this study revealed that, P. aeruginosa (Eb-21), B. subtilis (Rb-18) and T. harzianum can be used for plant growth promotion and management of Fusarium wilt of pigeonpea.
... The fungal mycelium, referred to as the spore germ tube, penetrates the root tips of healthy plants in contaminated soil [58]. It enters directly through wounds at the site of lateral root development [57]. Mycelium enters xylem vessels via pits after travelling through the cortex. ...
“Fusarium oxysporum f. sp. ciceris, the agent responsible for Fusarium wilt, poses a serious risk to the global production of chickpeas (Cicer arietinum L.). There are different races of this soil-borne pathogen, and each one has a different amount of virulence, which makes crop resilience difficult. Early yellowing and late wilting are two indicators of chickpea wilt that cause significant output losses. Complex genetic interactions are involved in chickpea resistance to Fusarium wilt. Resistance against particular pathogen races is conferred by a number of resistance genes, including h1, h2, and h3. Breeding procedures include both cutting-edge genomic techniques like marker-assisted selection (MAS) and traditional techniques like hybridization and backcrossing. By facilitating the accurate identification and stacking of resistance genes, MAS speeds up breeding. To treat this illness, it is essential to comprehend the genetic diversity of Fusarium wilt races, figure out the genetic basis of resistance, and use efficient breeding techniques. The goal of developing resilient chickpea varieties through the integration of genomic techniques and traditional breeding is to provide sustainable crop production in the face of changing disease problems”.
... Once pathogenic bacteria and other harmful microorganisms proliferate in the soil and increase in number, they will destroy the soil microecological environment and increase the incidence of diseases, thus affecting plants. Fusarium is considered to be the main pathogen causing "SARD" in China [21][22][23][24], and similar results were reported in orchards in South Africa [25]. ...
Due to the aging of trees, aged apple and cherry orchards need to be rebuilt urgently. However, due to the limitation of land resources, it is inevitable to rebuild the apple orchard by taking the aged cherry orchard as a replacement, which will lead to replant disease and seriously affect the sustainable development of the horticulture industry. This study investigated the effect of aged cherry orchard soil on the growth of M. hupehensis seedlings grown in pots, and it was further verified that allelochemicals in soil were one of the reasons for this effect. Three treatments were implemented: aged apple orchard soil (ppl), aged cherry orchard soil (pyl), and aged cherry orchard soil after fumigation with methyl bromide (pyz). Compared with pyz, pyl treatment significantly decreased the biomass, root growth, and antioxidant enzyme activity of M. hupehensis seedlings, and increased the content of MDA. Compared with ppl, pyl contains a smaller number of fungi and bacteria, but the abundance of the four disease-causing Fusarium remained high. In addition, the levels of allelochemicals found in the soil of aged cherry orchards can inhibit the normal growth and development of M. hupehensis seedlings. Amygdalin most strongly inhibited these seedlings. In summary, directly planting M. hupehensis seedlings in the soil of the aged cherry orchards still inhibits their normal growth and development, although the seedlings grow better than in aged apple orchard soil. Therefore, it is not feasible to directly plant M. hupehensis seedlings in the soil of aged cherry orchards, and measures should be taken to eliminate allelochemicals such as amygdalin and harmful microorganisms.
... Pseudomonas aeruginosa PNA1, P. chlororaphis PCL1391, and P. fluorescens 2-79 have been widely recognized for their biological activity against a number of phytopathogenic fungi and oomycetes through the biosynthesis of antibiotic derivatives such as phenazine-1-carboxylic acid (PCA), phenazine-1-carboxamide (PCN), and pyocyanin (Chin-A-Woeng et Anjaiah et al. 1998). Pseudomonas aeruginosa PNA1 isolated from the rhizosphere of chickpea has been known to exhibit biocontrol of phytopathogenic fungi such as Fusarium spp. on chickpea and pigeon pea, against Pythium splendens on bean and Pythium myriotylum on cocoyam (Anjaiah et al. 1998(Anjaiah et al. , 2003Tambong and Hofte 2001). Pseudomonas fluorescens 2-79 mutant strains with the inability to produce PCA provided significantly less protection against take-all disease on wheat seedlings (Thomashow and Weller 1988). ...
... Management of soil borne disease by single approach is difficult, uneconomical and integrated approach is the best way. Biological control is environment friendly and most accepted method used to control Fusarium oxysporum (Anjajah et al. 2003). Fungicides were used as seed treatment for seed borne diseases, as it eradicates the seed borne inoculums. ...
Fusarium wilt of chickpea, caused by Fusarium oxysporum f. sp. ciceris (Foc) is one of the major and economically
important disease. Integrated disease approach the best way for management of the disease by using fungicides and bio
agents. For this study, four potential Trichoderma asperellum isolates (Tr-1, Tr-6, Tr-10 and Tr-20), two potential fluo�rescent Pseudomonads i.e., Pseudomonas fluorescens (CRP-6 and CRP-8) and fungicides were selected. Six fungicides
evaluated against pathogen and effective fungicides were studied for compatibility with bio agents. Among the selected
bio agents T. asperellum (Tr-6) and P. fluorescens isolate (CRP-8) were found compatible with Vitavax power at 0.1%
under in vitro conditions, formulated as talc formulations and evaluated in different treatments under field conditions.
Pooled analysis results of two years indicated that among the 12 treatments imposed for Fusarium wilt, the treatment T6
(seed treatment with Vitavax power @ 1 g/kg and talc formulation of T. asperellum and P. fluorescens @ 8 g/kg of seed
and soil application of T. asperellum and P. fluorescens multiplied on FYM) has recorded more germination percentage
of 91.09, lower wilt incidence of 22.86% with higher yield of 1501 kg/ha and B:C ratio of 2.35:1 apart from resistant
check (T11) WR-315. It is followed by the treatments T9 (seed treatment with Vitavax power @ 1.0 g/kg of and talc for�mulation of T.asperellum @ 8 g/kg of seed and soil application of T.asperellum multiplied on FYM and drenching with
T. asperellum talc), T10 (seed treatment with Vitavax power @ 1.0 g/kg of and talc formulation of P. fluorescens @ 8 g/
kg of seed and soil application of P. fluorescens multiplied on FYM and drenching with P.fluorescens talc) and T4 (seed
treatment with Vitavax power @ 1.0 g kg-1 and talc formulation of T. asperellum @ 8 g kg-1 of seed and application of
mass multiplied T. asperellum on FYM) recorded low wilt incidence of 25.90%, 25.32% and 26.22% respectively and non
significant with each other in wilt incidence and yield. Untreated plot (T12) recorded high wilt incidence of 65.37% and
less yield of 543 kg/ha. It was concluded that the treatments T6 and T4 are considered as best treatments (though there
are other good treatments available) for management of Fusarium wilt of chickpea as they recorded higher B:C ratio, low
wilt incidence and higher yields.
... Management of soil borne disease by single approach is difficult, uneconomical and integrated approach is the best way. Biological control is environment friendly and most accepted method used to control Fusarium oxysporum (Anjajah et al. 2003). Fungicides were used as seed treatment for seed borne diseases, as it eradicates the seed borne inoculums. ...
Fusarium wilt of Chickpea is more problematic in chickpea grown areas. This article explains management of this disease by using potential biocontrol agents along with seed treatment chemicals
... Among these important chickpea diseases, FW affects the tap root system with the destruction of vascular bundles that impairs water transport to the shoot where symptoms such as (i) gradual wilting, (ii) floppy petioles, rachis, and leaflets, (iii) fading of green color occur prior to plant death (Iqbal et al. 2005;Mahmood et al. 2011). FW disease causes yield losses up to 100 per cent under favorable conditions (Anjaiah et al. 2003;Landa et al. 2004). ...
Fusarium wilt (FW) caused by the Fusarium oxysporum f. sp. ciceri is a devastating disease of chickpea (Cicer arietinum L.). To identify promising resistant genotypes and genomic loci for FW resistance, a core set of 179 genotypes of chickpea was tested for FW reactions at seedling and reproductive stages under field as well as controlled conditions in the greenhouse. Our results revealed that at seedling stage, most of the genotypes were found resistant whereas, at the reproductive stage majority of the genotypes were found susceptible. Genotyping using a 50K Axiom®Cicer SNP Array and trait data of FW together led to the identification of 26 significant (p≤E-05) marker-trait associations (MTAs) for FW resistance. Among 26 MTAs, 12 were identified using trait data recorded in the field (3 at seedling and 9 at reproductive stage) and 14 MTAs were identified using trait data recorded under controlled conditions in the greenhouse (6 at seedling and 8 at reproductive stage). The phenotypic variation explained by these MTAs varied from 11.75 to 15.86% with an average of 13.77%. Five MTAs were classified as major, explaining more than 15% phenotypic variation for FW and two MTAs were declared stable, being identified in either two environments or at two growth stages. One of the promising stable and major MTAs (Affx_123280060) detected in field conditions at reproductive stage was also detected in greenhouse conditions at seedling and reproductive stages. The stable and major (>15% PVE) MTAs can be used in chickpea breeding programmes.
... Studies by Anjaiah et al. (2003) showed the potential of P. aeruginosa as a biocontrol agent against Fusarium wilt of pigeonpea. Seed treatment with P. aeruginosa significantly reduced wilt incidence in susceptible and moderately tolerant pigeonpea genotypes. ...
Legumes are the important constituents of traditional healthy diets throughout the world, and second in agricultural
importance after cereals. The worldwide yield of legumes is unstable and limited due to susceptibility to diseases.
Vascular wilt disease caused by Fusarium oxysporum ff. spp. and Fusarium udum is a serious and major constraint in
legumes and causes up to 100% of yield loss. The use of microbial biological control agents (BCAs) is an effective,
environment-friendly, economical and sustainable approach to prevent Fusarium wilt in legumes. Research activities
were undertaken over the last two decades demonstrating the potential of microorganisms like Trichoderma spp.,
Pseudomonas spp., Bacillus spp., non-pathogenic F. oxysporum, and other bacteria and fungi as BCAs against
Fusarium wilt. BCAs with various modes of actions (hyperparasitism, antibiosis, induction of host resistance, and competition)
were evaluated for their biocontrol properties (production of antibiotics, lytic enzymes, antioxidant enzymes,
siderophore, and induction of host resistance), and applied alone or in combination, through different formulations,
delivery systems (seed, soil, and seed 1 soil) and altering parameters (host genotype, pathogen race, inoculum density,
BCA strain, temperature and sowing season, etc.), in the laboratory, greenhouse and field conditions to find out their
optimum efficiency. Study of these reports suggests that understanding the mechanism of actions requires immediate
attention, whereas, evaluation of BCAs under altered physiological and environmental conditions are needed. Further,
more field trials are crucial for the commercialization of effective BCAs. With the advancements of high-throughput
DNA sequencing and various omics approaches, these knowledge bases can be used for the commercialization of biological
control in the management of Fusarium wilt of legumes.
... Fusarium wilt of chickpea is prevalent in almost all chickpeagrowing areas of the world and its incidence varies from 14 to 32 % in the different states of India [8]. This disease causes yield losses up to 100 % under favorable conditions [9,10]. ...
Chickpea (Cicer arietinum) is one of the world’s major legume crops and suffers substantial damage from wilt disease incited by Fusarium oxysporum f. sp. ciceri (Padwick) with yield loss over 60 per cent. The screening for new resistance chickpea genotypes against this disease is an alternative approach to avoid indiscriminate use of chemical pesticides. In this study 55 chickpea genotypes were screened against Fusarium wilt. Out of 55 chickpea genotypes studied, only one genotype was found to be resistant and 12 were found to be moderately resistance. Nineteen genotypes showed moderately susceptible. However, nineteen and four genotypes showed susceptible and highly susceptible reaction for wilt disease, respectively.
... Neither the use of fungicides is usually effective as it is used mainly for the seed borne inoculum and the effect is short lived. Biological control using microorganisms provides an alternative to the use of synthetic fungicides with the advantages of reduced environmental impact, greater public acceptance and becoming a critically needed component of plant disease management, particularly in reducing root diseases (Meki et al., 2009;Anjajah et al., 2003;Landa et al., 2004b). These antagonists besides of helping to cope with plant diseases, they also provide batter nourishment to host plants (Glick, 1995;Burr et al., 1998). ...
Chickpea (Cicer arietinum L.) production is severely reduced by Fusarium wilt caused by Fusarium oxysporum f. sp. ciceris (Foc) in most chickpea growing areas worldwide. The effect of treating chickpea seeds with three bacterial strains of Bacillus and two strains of Pseudomonas to control wilt caused by this pathogen was carried out in plots under field conditions. The Bacillus strains had much better effect than Pseudomonas strains on plants health. Bacillus strain (K3) significantly increased seed germination, plant weight, number of pods and the yield. These were increased by (12, 21.2, 39.8 and 14.2%) respectively. Also, the strain B. amyloliquefaciens (5113) showed significantly increases of plant weight, number of pods and the yield (19.6, 19.9 and 10.1%) respectively. It can be concluded that bacterial seed coating combined with other control strategies as integrated pest management could be used successfully to control or at least decrease the effect of Fusarium wilt on chickpea production.
... It has been reported that bacterial strains covering plant roots act as the first line of defence for plants against disease invasion and reduce the risk for early or late wilting in plants (Wei et al., 2015). Previously, Actinomycetes, B. subtilis, and P. aeruginosa have been reported as efficient colonizers along with the roots of chickpea, and due to their good root colonization ability reduces the wilt incidences in chickpea (Anjaiah et al., 2003;Gopalakrishnan et al., 2015aGopalakrishnan et al., , 2015bSreevidya and Gopalakrishnan, 2017). Disease suppression in chickpea roots has been correlated with an increase in the growth of the root system (Akhtar and Siddiqui, 2008) and vice versa. ...
Chickpea is an important nutritive food crop both for humans and animals. Chickpea wilt caused by Fusarium oxysporum f.sp. ciceris (Foc) results in huge yield losses every year. Chickpea being a food crop requires the development of an eco-friendly bio-pesticide to effectively control the chickpea wilt disease. In this study, more than 50 bacterial stains isolated from the rhizosphere of healthy plants growing in wilt sick soil were examined for their Foc antagonist activities. Out of these, 17 strains showing >90% growth inhibition of Foc were then characterized for their plant growth-promoting (PGP) and biocontrol traits. The biocontrol and PGP traits identified include amylase, hydrogen cyanide, protease, cellulase, chitinase activities, p-solubilization, nitrogen-fixing, and indole-3-acetic acid production. Two bacterial strains, IR-27 and IR-57, exhibiting the highest Foc proliferation inhibition and the PGP potential along with a consortium of four different strains (Serratia sp. IN-1, Serratia sp. IS-1, Enterobacter sp. IN-2, Enterobacter sp. IN-6) were used for controlling the chickpea wilt disease and growth promotion of the chickpea plants. Confocal laser scanning microscopy revealed their root colonization ability with partial or complete elimination of broken Foc mycelia and hyphae from roots. The bacterial inoculations particularly the consortium significantly suppressed the disease and improved the overall root morphology traits (root length, root surface area, root volume, forks, tips, and crossings), resulting in enhanced growth of the chickpea plants. Significant changes in growth (107% increase in root length, 23% increase in shoot length, and 54% increase in branches) in Foc-challenged plants were observed when inoculated with the consortium. Further investigations revealed that the chickpea plants inoculated with bacterial strains induced the expression of a number of key defence enzymes, including the phenylalanine ammonia lyase, peroxidase, polyphenol peroxidase, β-1,3 glucanase, which might have helped the plants to thwart the pathogen attack. These findings indicate the potential of our identified bacterial strains to be used as a natural biopesticide for controlling the chickpea wilt disease.
... ciceris (FOC) and Rhizoctonia bataticola, respectively. Both the diseases have the potential to reduce the yield of chickpea up to 100 per cent (Anjaiah et al. 2003;Ghosh et al. 2014). The use of potentially hazardous fungicides in agriculture has been the subject of growing concern because of their possible adverse effects on the environment and the emergence of fungicide-resistant pathogens (Pal et al. 2001). ...
A total of 48 actinobacteria cultures isolated from Trans-gangetic plain zone of India were screened for their antagonistic potential against Rhizoctonia bataticola and Fusarium oxysporum f.sp. ciceris (FOC) using dual-culture plate assay. Percent growth inhibition resulted from different actinobacteria isolates against R. bataticola and FOC were found statistically significant with each other. Out of 48 actinobacteria isolates screened, thirteen and twelve actinobacteria isolates were found potential (>50% growth inhibition) against R. bataticola and FOC, respectively. Isolates, AIN 26 (Streptomyces puniceus IIPR:KR01:01) and AIN 56 (Streptomyces ginkgonis IIPR:HD01:05) showed highest growth inhibition (57.08% & 57.92%) and maximum inhibition zone (3.57cm & 3.62cm) against R. bataticola and FOC, respectively. Further, validation of the antagonistic potential of these actinobacteria isolates under greenhouse and sick field conditions have the potential for biological control of dry root rot and Fusarium wilt diseases in chickpea.
... Pigeonpea fields can be treated with fungal or bacterial agents (e.g., Serratia, Azotobacter, Clostridium, Bacillus, Arthrobacter, Alcarigens, Agrobacterium, Bradyrhizobium) which inhibit the proliferation of F. udum (Maisuria et al. 2008). Anjaiah, Cornelis, and Koedam (2003) reported a significant reduction in FW disease incidence in pigeonpea and chickpea after sowing seeds treated with a biocontrol strain of the bacterium Pseudomonas aeruginosa. ...
Combining ability analysis is fundamental in breeding programs to select desirable parents and progenies. The objectives of this study were to determine the combining ability effects, and gene action controlling agronomic traits and resistance to Fusarium wilt (FW) caused by Fusarium udum Butler in pigeonpea [Cajanus cajan (L.) Millspaugh]. Twenty-five progenies were developed from 10 selected parents using a 5 × 5 North Carolina Design II. The progenies and their parents were assessed for agronomic traits and FW resistance. The genotypes were subjected to artificial FW infection using a root dip inoculation technique to evaluate seedling resistance. ICEAP 87105 and ICEAP 01285 had significantly negative general combining ability (GCA) effects for days to 75% maturity (DTM), whereas MWPLR 22, Sauma and Mwayiwathualimi had positive GCA effects for grain yield (GYD) in a desirable direction. The study selected the best hybrids such as ICEAP 01285 × MWPLR 14 for early maturity, FW resistance and a high GYD, and TZA 5582 × ICEAP 00554, TZA 5582 × MWPLR 14, and Mwayiwathualimi × MWPLR 22 for FW resistance and a high GYD. The narrow-sense heritability values varied from 27% (number of seeds per plant) to 97% (DTM). Parental lines TZA 5582 and MWPLR 14 made strong contributions to desirable gene combinations that improved agronomic traits in the selected crosses. The new hybrids form novel breeding populations useful in improving the traits of economic importance in pigeonpea.
... Pyocyanin accounts for 90% of this bacterium's biocontrol ability (Feghali & Nawas, 2018;Waksman & Woodruff, 1940). It protects the host plants by inhibiting the growth of other soil pathogens (Anjaiah et al., 2003;Mahmoud et al., 2016). In addition, pyocyanin triggers induced systemic resistance of the host plant against various fungal pathogens (Audenaert et al., 2002;De Vleesschauwer et al., 2006). ...
Aim:
Pseudomonas aeruginosa, a leading opportunistic pathogen causing hospital-acquired infections, is predominantly present in agricultural settings. However, there are minimal attempts to examine the molecular and functional attributes shared by agricultural and clinical strains of P. aeruginosa. This study investigates the presence of P. aeruginosa in edible vegetable plants (including salad vegetables) and analyzes the evolutionary and metabolic relatedness of the agricultural and clinical strains.
Methods and results:
Eighteen rhizospheric and endophytic P. aeruginosa strains were isolated from cucumber, tomato, eggplant, and chili directly from the farms. The identity of these strains was confirmed using biochemical and molecular assays. The genetic and metabolic traits of these plant-associated P. aeruginosa isolates were compared with clinical strains. DNA fingerprinting and 16S rDNA-based phylogenetic analyses revealed that the plant- and human-associated strains are evolutionarily related. Both agricultural and clinical isolates possessed plant-beneficial properties, including mineral solubilization to release essential nutrients (phosphorous, potassium, and zinc), ammonification, and the ability to release extracellular pyocyanin, siderophore, and indole-3 acetic acid.
Conclusion:
These findings suggest that rhizospheric and endophytic P. aeruginosa strains are genetically and functionally analogous to the clinical isolates. In addition, the genotypic and phenotypic traits do not correlate with plant sources or ecosystems.
Significance and impact of the study:
This study reconfirms that edible plants are the potential source for human and animal transmission of P. aeruginosa.
... Worldwide chickpea yield loss due to Fusarium wilt caused by Fusarium oxysporum f.sp. ciceri (FOC) fluctuates from 10 to 90% and causes up to 100% loss in highly infested fields under favorable conditions [3][4][5]. Despite effective strategies adopted for disease control through chemical fungicides and resistant cultivars, development of latest pathogenic races and unrestrained use of synthetic agrochemicals constitute serious risk of environmental degradation [6]. On the other hand, global climate change will negatively influence crop production by exacerbating the prevalence of disease and diminish the efficacy of traditional approaches to disease control [7]. ...
To increase the chickpea production, chitosan nanoparticles (CNPs) were prepared from the cell membrane of Fusarium oxysporum f.sp. ciceri (FOC), a causal agent of Fusarium wilt in chickpea, and evaluated for its potential to induce defense responses and plant growth–promoting activity. Chickpea seeds treated with CNP enhanced shoot–root length, leaf number, and leaf size showing intensified photosynthetic activity and higher proline content. Foliar spray of CNP promoted plant growth and elicited the antioxidant enzymes in chickpea under pot condition. A significant increase in protein content was validated by localizing new polypeptides in SDS-PAGE analysis. In addition, CNP treatment showed a remarkable expression of defense enzymes offering protection to plants and also induced four new protease inhibitor isoforms. Furthermore, yield attributes were significantly higher in CNP-treated chickpea plants. As a cost-effective strategy, CNP prepared from cell membrane polymer of a phytopathogen holds great promise in establishing a replacement method for disease management and sustainable chickpea production.
... In a field trial, it was shown that the reduction of Fusarium wilt incidence in pigeonpea was up to 30% when soil was amended with T. harzianum at 10 g/ 9 m 2 . In another study by Anjaiah et al. (2003), it was found that the wilt incidence in pigeonpea was significantly reduced in susceptible and moderately tolerant genotypes by inoculation with Pseudomonas aeruginosa strain PNA1. Maisuria et al. (2008) had seen that 47% of wilt incidence in pigeonpea was reduced when the seeds were treated with Pantoea dispersa. ...
Pests and diseases amount to an estimated 1/sixth of farm produce losses globally each year, and overall losses in attainable yield due to pest and diseases are far greater in Asia and Africa impacting smallholder farmers’ ability to feed their families. In legumes, the production is severely affected by different species of soil-borne and foliar pathogens. Comprehensive detail of the R&D conducted on biotic stresses (diseases) in legumes with special reference to emerging diseases under changing climatic condition has been discussed in this article. Brief account of current distribution, economic importance and management strategy has also been discussed. The recent biotechnological approaches such as marker-assisted selection and genetic engineering are also being touched upon for managing these stresses.
... Ten isolates of actinomycetes were tested for antifungal activity against S. rolfsii under in vitro conditions using a dual culture assay (Anjaiah et al., 2003 andAdhilakshmi et al., 2013). Fresh cultures of actinomycetes were streaked on one end of the starch casein agar media plates and incubated for 96 h at 28 ± 2 ºC. ...
... by T. viride and P. fluorescens has been reported earlier by Madhukeshwara and Seshadri (2001), Malathi (2010), Rangeshwaran et al. (2002) and Yadav et al. (2007). It is reported that the antibiotics i.e. phenazine-1-carboxylic acid and oxychlororaphin have been found to contribute for the biocontrol of Fusarium wilt of crop plants (Anjaiah et al., 2003). Trichoderma viride was best in inhibiting the growth of F. solani in mulberry root rot by 73.6 per cent (Choudhari et al., 2012). ...
A study was conducted to know the efficacy of potential biocontrol agents and fungicides against mulberry wilt, Fusarium solani. Three antagonists viz., Trichoderma viride., Pseudomonas fluorescens and Bacillus subtilis and six fungicides viz., carbendazim, mancozeb, zineb, copper oxy chloride, tebuconazole and pre-mixture fungicide (carbendazim 75% + mancozeb 25%) were tested under in vitro and in pot culture against wilt pathogen. The results showed that Trichoderma and the bacterial bioagents significantly reduced the mycelial growth of the pathogen. Among the fungicides, mixture of carbendazim + mancozeb (0.1 %) completely inhibited the mycelial growth of the pathogen. In pot culture studies, the minimum (10.5 %) incidence of wilt was observed in soil drenching with carbendazim (0.1%) which was on par with soil application of consortia (Seri bed waste+Pf1+Bs4+Tv1+Neem cake) which showed 12.3 per cent incidence as compared to maximum (46.7 %) wilt incidence in control. Similarly, in field studies also recorded the minimum incidence in soil drenching with carbendazim (0.1%) followed by soil application with consortia.
... It is more prevalent in lower latitudes (0-30 o N) where growing season is relatively dryer and warmer than in the higher latitudes (30-40 o N). Fusarium wilt epidemics cause significant annual losses of chickpea yields (Halila andStrange, 1996, Jalali et al., 1992) that may reach 100 % under conditions favorable for disease (Anjaiah et al., 2003, Halila and Strange 1996, Navas-Cortes and Jimenez-Diaz 2000. Earlier wilting caused more loss than late wilting. ...
Chickpea wilt is one of the major limiting factors, for low yield of chickpea. In Pakistan chickpea wilt causes 10-50% losses every year. At all concentrations, Carbendazim and Benomyl proved most effective while Acrobat was least effective in suppressing the mycilial growth of the Fusarium oxysporum f. sp. ciceri. However, higher concentration of Acrobat was also slightly effective. Among the plant extracts, higher concentrations of Sufaida and Neem proved to be effective while onion failed to control the colony growth of Fusarium oxysporum f.sp. ciceri at all concentrations.
... Pseudomonas spp. Joshi et al., 2019, Vishwanathan et al., 2000 Mango Anthracnose T. asperellum, P. fluorescens Villalobus et al., 2013, Vivekananthan et al., 2004 Pigeon pea Wilt Trichoderma spp., P. fluorescens Kumar et al., 2009, Siddiqui et al., 2009 Chickpea Wilt T. harzianum, P. aruginosa Dubey et al., 2007, Anjaiah et al., 2003 Tomato Wilt, foot rot Trichoderma spp. Verma et al., 2017 12 Potato Dry rot, soft rot T. viride, T. harzianum Pseudomonas spp. ...
... Reason might be synthesis of PRP in control plants due to fungal infection (De Tapia et al., 1986;Tuzun et al., 1989;Ye et al., 1990;Meena et al., 2017h), Whereas increased sugar content in treated plant can be directly correlated to enhanced photosynthesis which in turn affect the growth of plant (Qazi et al., 2012;Sui et al., 2015). Several researchers have used various kind of bioformulations like PGPR based bioformulation, nano-particle based bioformulations (Rangeshwaran and Prasad, 2000;Srivastava et al., 2001;Chattopadhyay et al., 2001;Jana et al., 2001;Goel et al., 2002;Anjaiah et al., 2003;Ansari, 2005;Altindag et al., 2006;Kumar et al., 2007;Siddiqui, 2007, 2008;Usharani et al., 2009;Khare and Arora, 2010;Khare et al., 2011;Senthilraja et al., 2013;Choudhary et al., 2017;Kumari et al., 2018a, Kumari et al., 2018b but these approaches are very costly and time consuming as compared to the present approach of using a combination of plant extract, elicitor and binder. ...
Leaf spot disease caused by Curvularia lunata is one of the major constraints affecting the cultivation of maize in India. Recently, it has been reported that the severity of curvularia leaf spot was prevalent in moderate to severe intensities and cause extensive damage to the crop thus lowering the yields. In the present study, in vivo preventive effect of Lawsonia inermis Linn. bioformulation on curvularia leaf spot disease of maize has been studied. All the experiments were conducted in pots. Percent disease index (PDI), percent efficacy of disease control (PEDC), chlorophyll contents, total carotenoids, and others various growth characteristics like plant height, number of leaves per plant, total carbohydrate and protein content were recorded. Percent seed germination was also observed for seeds treated with all formulations. A significant control of leaf spot disease was recorded with bioformulations treatment T3 [seeds were treated with partially purified acetone extract (4 ml): 100% clove bud oil cake (4 ml): 100% cow dung (2 ml)], T4 [seeds were treated with partially purified acetone extract (3 ml): 100% clove bud oil cake (4 ml): 100% cow dung (3 ml)], T2 [seeds were treated with 100% alcoholic crude extract (2 ml): 100% clove bud oil cake (6 ml): 100% cow dung (2 ml)] and T1 [seeds were treated with 100% alcoholic crude extract (4 ml): 100% clove bud oil cake (4 ml): 100% cow dung (2 ml)] as compared to other bioformulation treatments and its PDI and PEDC were recorded 9.10%, 10.00%, 17.50%, 19.00% and 89.47%, 88.43%, 79.76%, 78.03%, respectively. Results showed that treatment with bioformulation treatment T3, notably increased plant height, number of leaves per plant, chlorophyll, carotenoids, and total soluble sugar content followed by formulations number T4, T2, and T1. However, total soluble protein content was observed to be less in T3 as compared to control. This study suggests that these bioformulations could be essential towards sustainable agricultural science deprived of harming the ecosystem. The synthesized bioformulations have enormous potential to be commercially explored for agriculture use.
... Most of the Ethiopian soils contain low nutrient content due to erosion and absence of nutrient recycling. In addition, most of the areas used for production of grains especially tef, wheat and barley fall under the low fertility soils [62][63][64][65][66][67][68][69][70][71][72][73][74][75]. Frequent use of chemical fertilizers and narrow crop rotation can cause declining microbial biodiversity and soil fertility [75][76][77][78][79][80][81][82][83][84][85]. ...
Teff (Eragrostis tef) supports more than 60-75% of Ethiopia’s population as staple and co-staple food. Interest in teff has increased noticeably
due to its very attractive nutritional profile and gluten-free nature of the grain. Teff farming practice varies in different growing areas. Study
objective was to assess and document farmer’s traditional knowledge of teff farming and utilization practice. Data was collected using structured,
semi-structured questionnaire from 172 listed elder informants. Teff farming steps and farming area preparation, cultivated teff variety, the role
of crop rotation, type of agroforestry, traditional threshing, type of crop used for rotations, role of microbes in soil fertility, farming equipment,
storage and piling practice were described. Among the respondents 91.86% were male and 8.14% female. Teff variety currently cultivated by
many farmers are Magna, Sergegna, Bunign, kuncho, Qoreta, Bost, Package, Oromia, Shenkore, Cross37, Kora. 96% of respondent used cop
rotation for teff farming and productivity. These are Lathyrus sativus, Phaseolusvulgaris, Pistum stvium, Lensculinaris, Cicer arietinum, Zeamays,
Triticum aestivum, Hordeum vulgare, Allium cepa, Trigonella foenum-graecum. Teff productivity differed in the type of crop used for rotation, in
average 3000Kg/hectar, 2625Kg/hektar, 2230Kg/hektar, 1700-2000Kg/hektar is obtained from crop rotated by Onion, Common bean, Chickpea
and Lentil respectively. This traditional knowledge in using of legume & cereal plant for crop rotation in teff productivity confirms that farmers
indirectly enrich plant growth promoting microbes. These are, Acinetobacter, Agrobacterium, Bacillus, Burkholderia, Chryseomonas, Enterobacter,
Pseudomonas, Rhizobium spp. involved in Nitrogen fixation, phosphate solubilization, Phytohormon, sidrophore and Antibiotics production.
... Fusarium wilt of chickpea has also been reported in many countries of the world (Shakoor, 1991, being more prevalent in lower latitudes (0-300N) where growing season is dryer and warmer than the higher latitudes. Wide spread occurrence of chickpea wilt disease throughout the world cause a considerable annual loss to chickpea production (Halila andStrange, 1996 andJalalali andChand, 1992) that might reach up to 100 % under conditions favorable for disease (Anjaiah et al., 2003;Navas-Cortes et al., 2000). The production of chickpea in California declined largely because of chickpea wilt (Buddenhagen et al., 1988). ...
Chickpea wilt caused by Fusarium oxysporum f.sp. ciceris (Padwick) is a devastating disease of the chickpea crop throughout the world, wherever, chickpea is grown. Soil / environmental factors play an important role for wilt disease development. For successful and economical management characterization of soil and environmental factors conducive for wilt disease development and identification of resistant sources within available germplasm against wilt disease are very important. Three hundred and eighteen genotypes obtained from various sources were evaluated under sick plot conditions against chickpea wilt disease incidence. The experiment was planted in augmented design with single replication, repeated twice during the years of 2010-11 and 2011-12. Natural inoculums was relied upon for infection based upon a disease rating scale and area under disease progressive curve, only three lines/varieties (5006, k021-10 and k035-10) were found to be highly resistant during the both years of investigation. Most of the lines/varieties were moderately resistant to susceptible (21-50% Disease incidence). A significant co-relation of environmental/ soil variables (i.e. maximum and minimum air temperature, relative humidity, rainfall soil max. /min. temperature and soil moisture) with disease incidence was recorded on 40 chickpea lines. Maximum disease development occurred at temperature range of 23-28 . For the management of chickpea wilt disease fungicides and biological control agents were used both in vitro and glass house assay. In-vitro study showed that Carbendazim proved to be best among the fungicides, while among the bio-control agents Pseudomonas fluorescens was more efficient against Fusarium oxysporum f.sp. ciceris. These treatments also proved effective in glass house by lowering the number of chickpea wilted plants.
... Among them, Trichoderma spp. is one which is evaluated because of its potential alternative of the commercial fungicides like thiram, bavistin, benomyl, etc., against many soilborne and foliar fungal pathogen. In recent years, several species of Trichoderma are used as biocontrol agents/biopesticide against fungal diseases of plants (Upadhyay and Rai, 1981;Bhatnagar, 1996;Somasekhara et al., 1996Somasekhara et al., , 1998Gundappagal and Bidari, 1997;Biswas and Das, 1999;Prasad et al., 2002;Khan and Khan, 2002;Anjaiah et al., 2003;Sawant et al., 2003;Roy and Sitansu, 2005;Dhar et al., 2006;Maisuria et al., 2008;Ram and Pandey, 2011). Trichoderma usually grows in its natural habitat on the root surface, and so affects root disease in particular, but is also effective against foliar diseases of the crops. ...
... The role of pyocyanin from P. aeruginosa 7NSK2 strain, in inducing resistance to Botrytis cinerea that causes infection in tomato and grapevine was demonstrated by Audenaert et al. [56]. Also, Anjaiah et al. [57] reported that pyocyanin from Pseudomonas species isolated from rhizosphere soil were used as biocontrol agent against Fusarium, the causative agent of wilt of chickpea and Pythium damping of bean. ...
Phyllosphere colonizing antagonistic bacterial isolates were evaluated for managing major rice foliar diseases, namely brown spot caused by Bipolaris oryzae and sheath rot caused by Sarocladium oryzae. Among these various isolates, Pseudomonas aeruginosa isolate 1 effectively inhibited the mycelial growth of B. oryzae and S. oryzae. The volatile compounds of Bacillus subtilis isolates effectively inhibited the mycelial growth of S. oryzae and B. oryzae . Non‐volatile compounds of P. aeruginosa isolate 2 and B. subtilis isolate 1 recorded the maximum inhibition of mycelial growth of B . oryzae and S. oryzae , respectively. P. aeruginosa isolates produced fluorescent pigments and hydrogen cyanide (HCN), whereas isolates of Bacillus spp. did not. All the isolates of P. aeruginosa and Bacillus spp. produced protease enzymes. P. aeruginosa isolates solubilized phosphate, whereas isolates of Bacillus spp. did not. Rice seeds treated with these bacterial suspensions showed improvement in plant growth parameters. The foliar application of two bacterial strains, namely P. aeruginosa isolate 1 + B. subtilis isolate 1 recorded the minimum brown spot and sheath rot disease incidence. Thus, the present showed that phyllosphere colonizing P. aeruginosa and B. subtilis have the potential application for managing foliar fungal diseases of rice plants.
Pseudomonas aeruginosa is one of the most versatile bacteria with renowned pathogenicity and extensive drug resistance. The diverse habitats of this bacterium include fresh, saline and drainage waters, soil, moist surfaces, taps, showerheads, pipelines, medical implants, nematodes, insects, plants, animals, birds and humans. The arsenal of virulence factors produced by P. aeruginosa includes pyocyanin, rhamnolipids, siderophores, lytic enzymes, toxins and polysaccharides. All these virulent elements coupled with intrinsic, adaptive and acquired antibiotic resistance facilitate persistent colonization and lethal infections in different hosts. To date, treating pulmonary diseases remains complicated due to the chronic secondary infections triggered by hospital-acquired P. aeruginosa . On the contrary, this bacterium can improve plant growth by suppressing phytopathogens and insects. Notably, P. aeruginosa is one of the very few bacteria capable of trans-kingdom transmission and infection. Transfer of P. aeruginosa strains from plant materials to hospital wards, animals to humans, and humans to their pets occurs relatively often. Recently, we have identified that plant-associated P. aeruginosa strains could be pathologically similar to clinical isolates. In this review, we have highlighted the genomic and metabolic factors that facilitate the dominance of P. aeruginosa across different biological kingdoms and the varying roles of this bacterium in plant and human health.
The third-most important food legume in terms of economic importance worldwide is the chickpea (Cicer arietinum L.). Its potential production is frequently constrained by numerous biotic stressors, such as bacterial and viral infections, the nematodes, insects Ascochyta blight, fusarsium wilt, and botrytis grey mould are the three major fungal diseases that cause significant economic losses, while Helicoverpa armigera, Aphis craccivora, cowpea weevil are the three major pre-harvest pest of chickpea. Several biological, chemical, cultural, agronomical practices use to control biotic stress, apart from that few modern biotechnological approaches also develop for high yielding and biotic stress resistant varieties. This paper aims to discuss about different biotic stresses and their management strategies and different role of plant growth promoting rhizobacteria in controlling biotic stress.
Pigeon pea, also known as Cajanus cajan, ranks as the fifth most crucial grain legume globally and represents a valuable protein source for vegetarians. However, the inconsistency in its yield is a persistent challenge, primarily stemming from its vulnerability to various pests and diseases. One of the most devastating among these adversaries is Fusarium wilt, which can result in staggering yield losses of up to 100% and can afflict pigeon pea crops across all growing seasons. Compounding the problem, the pathogen responsible for Fusarium wilt is soil-borne, capable of enduring in the soil for extended periods, rendering it a formidable and persistent threat to pigeon pea cultivation. In the context of this book chapter, our aim is to delve into the present state of knowledge regarding Fusarium wilt in pigeon pea, the characteristics and behaviour of the pathogen responsible, and to explore strategies that can effectively mitigate yield losses. To address this challenge comprehensively, we propose a multifaceted approach that combines various agronomic practices, the development and utilization of resistant pigeon pea varieties, the intentional deployment of biocontrol agents, reduced reliance on chemical fungicides, and the exploration of innovative disease management techniques. By amalgamating these approaches, we aim to provide a holistic framework for effectively managing Fusarium wilt in pigeon pea crops, ultimately ensuring more stable and productive harvest.
Pigeon pea is one of the most significant legume crops in India.As it revitalises soil fertility by fixing atmospheric nitrogen, it is given a crucial role in agricultural systems and is widely used by many small and marginal farmers in developing nations. Wilt (Fusarium udum), a soilborne disease, has a major negative impact on crop productivity. Wilt can affect plants at any stage, but it's most common during the flowering and podding phases. All of the major pigeon pea-growing regions in the globe experience severe losses as a result of this disease. The soilborne pathogen enters the plant through the roots, moves up the water transport system to the xylem vessels, and then moves on to the stem and leaf. It is crucial to be concerned about the disease's prevalence, severity, and interactions with the host and its pathogens. The wilt disease in pigeon pea can be treated using a variety of conventional methods as well as chemical and biological methods. Understanding the molecular interactions between the host and the pathogen as well as the use of biotechnological tools together with biological approaches are necessary for managing Fusarium udum in pigeon pea fields. Traditional management techniques are getting less attention, and there are more ecological, economic, and social problems linked to the overuse of chemical pesticides. Additionally, there is a lack of knowledge on how pigeon pea fusarium wilt resistance is inherited, which has a significant impact on crop development projects. Important management techniques, both conventional and biotechnology, have been covered in this chapter along with their effects on pigeon pea wilt disease. The environmental factors, such as soil type, temperature, and nutrient availability, that have been shown to have an impact on the Fusarium population have also been discussed.
Spośród poznanych dotychczas ponad 10000 hodowalnych gatunków bakterii, ponad 150 powoduje choroby roślin. Ze względu na ich objawy fitopatogeny bakteryjne dzieli się na nekrogeny, macerogeny i onkogeny. Niektóre z nich wykazują zdolność zakażania organizmów spoza królestwa roślin, w tym człowieka. Poważnym zagrożeniem jest także kontaminacja roślin i gleby przez wyłączne patogeny człowieka i/lub zwierząt. Są to głównie bakterie jelitowe. W środowisku roślin występują również bakterie korzystnie oddziałujące na ich zdrowotność, wzrost i plonowanie. Bakterie takie dysponują mechanizmami, które umożliwiają bezpośrednie i/lub pośrednie ograniczanie sprawców chorób, wykazując wobec nich aktywność antagonistyczną, a możliwie także indukując odporność roślin na porażenie. Ich zastosowanie w praktyce wymaga jednak przeprowadzenia szczegółowych badań, bowiem nawet te same szczepy mogą korzystnie oddziaływać na rośliny, a jednocześnie stanowić różnego rodzaju zagrożenia. I chociaż ochrona roślin metodą biologiczną jest obiecującą perspektywą, to ważne jest, aby mieć w polu widzenia jej możliwy, bezpośredni lub pośredni, negatywny wpływ na środowisko i zdrowie ludzi.
Background
P.aeruginosa, has been frequently connected to immune-compromised individuals. Dynamic electrochemical metabolite assists in the creation of biofilms, the production of genes, and the maintenance of bacterial cells. The bacteria produce several phenazine derivatives, as well as the blue-green pigment pyocyanin, which works as a signalling molecule in quorum signalling and virulence factors.
Objective
This review paper intends to give information on the compound's history, virulence mechanism, current biological horizon opened, as well as antagonism and bio-control actions in other bacteria. Current industrial trends and the prospects of pyocyanin-based development were also analysed.
Methods
A bibliographic search of scientific literature published up to 2020 was conducted using scientific databases and search engines. Pyocyanin, phenazine, Pseudomonas, virulence, quorum signalling, health, in vivo, and clinical investigations were among the keywords used in various combinations. The data were retrieved independently from eligible papers using the usual data extraction approach.
Results
Due to pyocyanin's antibacterial properties, the pharmaceutical industry is predicted to grow faster than other businesses. P.aeruginosa which has had its respiratory chain altered by protonated 3,5-dichlorophenol in water can be used as a biosensor. Cellular systems exposed to the chemical experience increased oxidative stress, which leads to gradual apoptosis. Pyocyanin is engaged in bacterial signalling processes, influencing colony shape and alarming innate immune cells.
Conclusion
Focused research on the virulence factor is required, as the specific contribution remains unknown. The link between biological and therapeutic features needed well description to determine the precise action mechanism(s) to design novel medications.
Plant growth-promoting rhizobacteria (PGPR) are being used as an alternative approach to combat plant diseases. About 80–90% of plant diseases are caused by bacterial and fungal pathogens, which remain an inevitable cause for the loss of several crops. Phytopathogenic bacteria and fungi are the major constraints to sustainable agriculture by adversely affecting crop growth and productivity. Owing to the increased pollution and harmful impacts of chemicals to control these pathogens, scientists are now centering on safer biological organisms and their byproducts. Secondary metabolites and volatile organic compounds (VOCs) emitted by various beneficial bacterial strains have a lot of potential for enhancing plant growth and preventing plant diseases. The VOCs produced by the most researched bacterial strains, such as Pseudomonas genera, are well recognized for protecting economically imperative plants and inducing resistance against bacterial and fungal phytopathogens. This chapter concentrates on throwing up a better grasp of biological activities of secondary metabolites such as hydrogen cyanide, siderophores, antibiotics, and VOCs produced by Pseudomonas spp. Hundreds of various bacterial VOCs, including alcohols, terpenoids, esters, and sulfur compounds, have been discovered. The VOCs emitted by Pseudomonas sp., for instance, acetophenone, 1,3-butadiene, 2-undecanone, benzaldehyde, 1,2-benzisothiazol-3(2H)-one, dimethyl trisulfide, dimethyl disulfide, benzothiazole, nonanal, N,N-dimethyldodecylamin, 3,5,5-trimethyl-1-hexanol, isovaleric acid, cyclohexanol, 2-ethyl 1-hexanol, n-decanal, decyl alcohol, etc., are reported for their antagonistic potential, inducing resistance in host plants against several bacterial and fungal pathogens. Crop growth enhancement and protection via VOCs is a promising and an ecofriendly method, substituting the harmful impacts of chemicals and ensuring the long-term sustainability in agriculture.
Chickpea wilt, caused by Fusarium oxysporum f. sp. ciceris, is a disease that decreases chickpea productivity and quality and can reduce its yield by as much as 15%. A newly isolated, moss rhizoid-associated Pseudomonas aeruginosa strain A7, demonstrated strong inhibition of Fusarium oxysporum f. sp. ciceris growth. An in vitro antimicrobial assay revealed A7 to suppress the growth of several fungal and bacterial plant pathogens by secreting secondary metabolites and by producing volatile compounds. In an in vivo pot experiment with Fusarium wilt infection in chickpea, the antagonist A7 exhibited a disease reduction by 77 ± 1.5%, and significantly reduced the disease incidence and severity indexes. Furthermore, A7 promoted chickpea growth in terms of root and shoot length and dry biomass during pot assay. The strain exhibited several traits associated with plant growth promotion, extracellular enzymatic production, and stress tolerance. Under aluminum stress conditions, in vitro growth of chickpea plants by A7 resulted in a significant increase in root length and plant biomass production. Additionally, hallmark genes for antibiotics production were identified in A7. The methanol extract of strain A7 demonstrated antimicrobial activity, leading to the identification of various antimicrobial compounds based on retention time and molecular weight. These findings strongly suggest that the strain’s significant biocontrol potential and plant growth enhancement could be a potential environmentally friendly process in agricultural crop production.
Apple replant disease (ARD), caused largely by soil-borne fungal pathogens, has seriously hindered the development of the apple industry. The use of antagonistic microorganisms has been confirmed as a low-cost and environmentally friendly means of controlling ARD. In the present study, we assessed the effects of Bacillus amyloliquefaciens QSB-6 on the growth of replanted apple saplings and the soil microbial environment under field conditions, thus providing a theoretical basis for the successful use of microbial biocontrol agents. Four treatments were implemented in three apple orchards: untreated replant soil (CK1), methyl bromide fumigation (CK2), blank carrier treatment (T1), and QSB-6 bacterial fertilizer treatment (T2). The plant height, ground diameter, and branch length of apple saplings treated with T2 in three replanted apple orchards were significantly higher than that of the CK1 treatment. Compared with the other treatments, T2 significantly increased the number of soil bacteria, the proportion of actinomycetes, and the activities of soil enzymes. By contrast, compared with the CK1 treatments, the phenolic acid content, the number of fungi, and the abundance of Fusarium oxysporum, Fusarium moniliforme, Fusarium proliferatum, and Fusarium solani in the soil were significantly reduced. PCoA and cluster analysis showed that soil inoculation with strain QSB-6 significantly decreased the Mcintosh and Brillouin index of soil fungi and increased the diversity of soil bacteria in T2 relative to CK1. The soil bacterial community structure in T2 was different from the other treatments, and the soil fungal communities of T2 and CK2 were similar. In summary, QSB-6 bacterial fertilizer shows promise as a potential bio-inoculum for the control of ARD.
Pseudomonas aeruginosa, a leading opportunistic pathogen causing hospital-acquired infections is predominantly present in agricultural settings. There are minimal attempts to examine the molecular and functional attributes shared by agricultural and clinical strains of P. aeruginosa. This study aims to investigate the presence of P. aeruginosa in edible vegetable plants (including salad vegetables) and analyze the evolutionary and metabolic relatedness of the agricultural and clinical strains. Eighteen rhizospheric and endophytic P. aeruginosa strains were isolated from cucumber, tomato, eggplant, and chili directly from the farms. The identity of these strains was confirmed using biochemical, and molecular markers and their genetic and metabolic traits were compared with clinical isolates. DNA fingerprinting analyses and 16S rDNA-based phylogenetic tree revealed that the plant- and human-associated strains are evolutionarily related. Both agricultural and clinical isolates possessed plant-beneficial properties, including mineral solubilization (phosphorous, potassium, and zinc), ammonification, and the ability to release extracellular siderophore and indole-3 acetic acid. These findings suggest that rhizospheric and endophytic P. aeruginosa strains are genetically and functionally analogous to the clinical isolates. This study highlights the edible plants as a potential source for human and animal transmission of P. aeruginosa.
The application of endophytic bacteria, particularly members of the genus Bacillus, offers a promising strategy for the biocontrol of plant fungal diseases, owing to their sustainability and ecological safety. Although multiple secondary metabolites that demonstrate antifungal capacity have been identified in diverse endophytic bacteria, the regulatory mechanisms of their biosynthesis remain largely unknown. To elucidate this, we sequenced the entire genome of Bacillus amyloliquefaciens GKT04, a strain isolated from banana root, which showed high inhibitory activity against Fusarium oxysporum f. sp. cubense race 4 (FOC4). The GKT04 genome consists of a circular chromosome and a circular plasmid, which harbors 4,087 protein-coding genes and 113 RNA genes. Eight gene clusters that could potentially encode antifungal components were identified. We further applied RNA-Seq analysis to survey genome-wide changes in the gene expression of strain GKT04 during its inhibition of FOC4. In total, 575 upregulated and 242 downregulated genes enriched in several amino acid and carbohydrate metabolism pathways were identified. Specifically, gene clusters associated with difficidin, bacillibactin, and bacilysin were significantly upregulated, and their gene regulatory networks were constructed. Our work thereby provides insights into the genomic features and gene expression patterns of this B. amyloliquefaciens strain, which presents an excellent potential for the biocontrol of Fusarium wilt.
The potential of phenazine-producing strains for the management of fungal and oomycete plant pathogens has been reviewed for the first time. Isolated natural phenazines showed similar, or even higher, antifungal activity in comparison with commercial fungicides. The occurrence and concentration of phenazines strongly depended on the studied strains and the antifungal activity of the strains was found to be dependent on the biosynthesis of phenazines. Except for phenazine-1-carboxylic acid (PCA), most phenazines were found in the secretions below their minimum inhibitory concentrations (MIC) and, in general, most strains showed low in vivo inhibitory activities, observing the highest biocontrol ability when using PCA-producing Pseudomonas chlororaphis and P. fluorescens. Most reports focused on the study of Pseudomonas, reducing the structural diversity, and limited the biocontrol screenings to root diseases. The conclusions achieved in this work help to understand the current state of the research field, and reveal new insights on the development of efficient biocontrol strategies using phenazine-producing strains.
In the present study preparation of different bioformulations of Lawsonia inermis Linn. (Henna) leaves and its in vitro antifungal activity were evaluated against Curvularia lunata (Wakker) Boedijn caused leaf spot disease in maize. Thirty herbal formulations were prepared using plant extracts, elicitor and binder, and assayed for antifungal activity by poison food technique. Among all the bioformulations, optimum activity was observed in formulation number 4, 12, 19 and 28 i.e. 77.82%, 79.84%, 83.47% and 81.45%, respectively, against C. lunata. On the basis of results obtained, best bioformulation will be used for eco-friendly in vivo control of disease.
Pigeon pea [(Cajanus cajan) (L.) Millsp.], commonly known as red gram or tur dal, holds the second position as pulse crop in India which is also a vital food legume crop in semi-arid regions worldwide. It is a highly essential component of our diet because of its high protein content. The crop has a prominent difference between the potential and actual yield, and this huge difference is because of the number of biotic and abiotic factors on the crop which includes shortage of improved quality cultivars in pigeon pea-growing regions. The major biotic stresses that limit pigeon pea production include various fungal pathogens, but out of them, only a few fungal diseases like fusarium wilt caused by Fusarium udum Butler. Phytophthora blight caused by Phytophthora drechsleri Tucker f. sp. cajani, Macrophomina root rot caused by Macrophomina phaseolina (Tassi) Goid and Alternaria blight caused by Alternaria alternata are responsible for the substantial damage of the crop. Various techniques are involved in the suppression of plant pathogens and for improving the quality and quantity of the crop. Biocontrol agents, such as Trichoderma sp., Bacillus sp. and Pseudomonas sp. individually and in microbial consortium, not only reduce the disease severity but also enhance the growth and productivity of the crop. Based on these beneficial plant-microbe interactions and their mode of action against plant pathogens, bioformulations of microbial consortium can be used as biofertilizers and also as plant strengtheners. The present study discusses the lasting solution by exploiting the best biotechnological approaches for the development of economically viable and sustainable effective management of fungal diseases of pigeon pea.
Pigeonpea (Cajanus cajan (L.) Millisp.) is an economically important grain legume of the tropical and subtropical region of the world and is one of the major inseparable dietary protein sources to the large mass of the Indian population. The diverse growing condition exposes the pigeonpea to different biotic and abiotic stresses during its life cycle. Pigeonpea get infected by various diseases nevertheless, only a few of them are of economic importance. After wilt (C.O: Fusarium udum) and sterility mosaic disease (C.O: Pigeonpea Sterility Mosaic Virus), Phytophthora stem blight (PSB) caused by Phytophthora drechsleri Tucker f. sp. cajani is the third most potentially important disease of pigeonpea in India. This disease is soilborne; the fungus survives as chlamydospores, oospores, and dormant mycelium in the soil and on infected plant parts. Moist cloudy weather with drizzling rain for about 6–8 hrs (RH = 85–95%) with temperatures around 25 °C favor disease development. The disease can be managed through agronomic interventions like early sowing, ridge planting, and summer ploughing of field to desiccate pathogen. The seed treatment and spraying of Ridomil MZ® at 3 g/kg seed and 2 g/liter of water, respectively, may give protection, but its efficacy is doubtful. Therefore, the development of resistant varieties would be an effective means to control the disease. This chapter describes the effect of P. drechsleri on pigeonpea and its productivity and will also describe the methods used in controlling the stem blight of pigeonpea.
Pigeon pea (Cajanus cajan L. Millsp.) is one of the leading pulses crops of India under the Leguminaceae family. It is grown as an annual and perennial crop under rainfed conditions, mostly in less fertile or marginal areas intercrop with cereals and oilseeds. The circumstances under which the crop is cultivated pose a major barrier for the crop, making it sensitive to abiotic and biotic stresses, and a key drawback in the maximum yield potential. Among the abiotic stresses, temperature, soil acidity, salinity, drought, waterlogging, etc. cause severe yield losses, and major biotic stresses include diseases like wilt, Phytophthora blight, Alternaria blight, etc. The crop is also susceptible to various parasitic nematodes, viz. Meloidogyne javanica, Heterodera cajani, Rotylenchus sp., etc. Pigeon pea has the specialty of biological nitrogen fixation (BNF) and efficiently establishes symbiosis with Bradyrhizobium spp. even though the crop is a promiscuous legume. This symbiosis provides more than 90% of nitrogen requirement for the crop depending on the conduciveness of the growing environment, variety of crop and type of soil. To be productive, the crop also requires neutral to slightly acidic soil conditions, and the potential yield is significantly reduced under extreme conditions of acidity, basicity or salinity, drought, etc. As the saying goes, “When the soil is deficient, the plants also are deficient and weakened, and they lose their defenses” (Charlotte Gerson). So, maintaining the soil health by supplying all the essential nutrients in the form of organic or inorganic manures is crucial for the crop to remain healthy and productive. Therefore, the efficient and improved practices of nutrient management like an application of cross-inoculants’ group-specific biofertilizers, enriched compost, liming of acid soils or gypsum application in alkaline soils can be practised for sustaining the soil health. Deep summer ploughing, soil solarization, biopesticides, etc. are some of the pathogen management practices for maintaining the health of the crop and, thus, reduction in yield losses.
Pigeon pea [Cajanus cajan (L.) Millsp.] is one of the important legume crops in India, and more than 100 pathogens such as fungi, bacteria, nematodes, and viruses attack this crop, and among which the vascular wilt pathogenic fungus Fusarium udum is economically extremely damaging. Seedling and adult plants show the symptoms of fusarium wilt with yellowing and drying of leaves followed by whole plant wilting. Wilted plants can be easily recognized in the field with wilt patches. Wilt occurs at the seedling stage of plants but is mainly seen at flowering and podding stages. This disease causes significant loss in all the major pigeon pea-growing areas all over the world. Being soilborne, the pathogen enters the plant through the roots and reaches the xylem vessels along with the water transport system and subsequently reaches the stem and foliage. The incidence and severity of the disease along with understanding the host-pathogen interaction are of great concern. There are many traditional strategies as well as chemical and biological approaches for managing the wilt disease in pigeon pea. Lesser emphasis on the traditional strategies and increasing ecological, economic, and social problems arising with excessive application of chemical pesticides emphasize the need to understand molecular interactions between the host and the pathogen and application of biotechnological techniques along with biological approaches for managing Fusarium udum in pigeon pea fields. Also, there is a limited understanding of the inheritance of fusarium wilt resistance in pigeon pea which is greatly affecting crop improvement programs. In this chapter, we have discussed important strategies from traditional to biotechnological with their impact on the management of wilt disease in pigeon pea. We have also discussed the environmental factors such as soil type, temperature, and nutrient availability which have been shown to affect Fusarium population.
In the present study, the effects of the arbuscular my-corrhizal fungus (AMF) Glomus intraradices Schenck & Smith and four rhizobacteria (RB; 58/1 and D/2: Pseudomonas fluorescens biovar II; 17: P. putida; 21: Enterobacter cloacae), which are the important members of the rhizosphere microflora and biological control agents against plant diseases, were examined in the pathosystem of Fusarium oxysporum f. sp. lycoper-sici [(Sacc) Syd. et Hans] (FOL) and tomato with respect to morphological parameters (fresh and dry root weight) and phosphorous (P) concentration in the roots. Treatments with single and dual inoculation with G. intraradices and RB strains reduced disease severity by 8.6–58.6%. Individual bacteria inoculations were more effective than both the single AMF and dual (G. intraradices + RB) inoculations. In addition, the RB and G. intraradices enhanced dry root weight effectively. Significant increases in root weights were recorded particularly in the triple inoculations compared with single or dual inoculations. Compared with the non-treated controls all biological control agents increased P-content of treated roots of plants. Colon-ization with RB increased especially in triple (FOL + G. intraradices + RB) inoculations whereas colonization of G. intraradices was significantly decreased in treatment of FOL + G. intraradices compared with triple inoculations. The results suggest that suitable combinations of these biocontrol agents may ameliorate plant growth and health.
Pseudomonas aeruginosa PGPR2 was found to protect mungbean plants from charcoal rot disease caused by Macrophomina phaseolina. Secondary metabolites from the culture supernatant of P. aeruginosa PGPR2 were extracted with ethyl acetate and the antifungal compound was purified by preparative HPLC using reverse phase chromatography. The purified compound showed antifungal activity against M. phaseolina and other phytopathogenic fungi (Fusarium sp., Rhizoctonia sp. Alternaria sp., and Aspergillus sp.). The structure of the purified compound was determined using (1)H, (13)C, 2D NMR spectra and liquid chromatography-mass spectrometry (LC-MS). Spectral data suggest that the antifungal compound is 3,4-dihydroxy-N-methyl-4-(4-oxochroman-2-yl)butanamide, with the chemical formula C14H17NO5 and a molecular mass of 279. Though chemically synthesized chromanone derivatives have been shown to have antifungal activity, we report for the first time, the microbial production of a chromanone derivative with antifungal activity. This ability of P. aeruginosa PGPR2 makes it a suitable strain for biocontrol.
Fluorescent pseudomonads are involved in the natural suppressiveness of some soils to fusarium wilts. These bacteria have been applied successfully to suppress fusarium wilts of various plant species grown in conducive soils and growing substrates. Suppression of fusarium wilts by fluorescent pseudomonads can be ascribed to direct and indirect effects against pathogenic Fusarium oxysporum. Direct effects are expressed by a reduction of the saprophytic growth of the pathogen leading to delay and reduction of root infections. This antagonism was demonstrated to be related to siderophore‐mediated iron competition. Iron competition was also shown to enhance the antagonistic effect of non‐pathogenic F. oxysporum by making the pathogen more susceptible to fungal competition for carbon. Indirect effects of fluorescent pseudomonads against pathogenic F. oxysporum are mainly related to the induction of host plant resistance which can be associated with the bacterial lipopolysaccharides. Suppression of fusarium wilts by some fluorescent pseudomonads could also be related to their ability to detoxify fungal metabolites such as fusaric acid. Association of different mechanisms of suppression increases the efficacy and consistency of the biological control under various experimental conditions. Increased knowledge of mechanisms of suppression now enables management of the environment, to some extent, to favour expression of the beneficial activities. These activities are only expressed if the bacterial density is sufficiently high.
Aims:
Screening of bacterial flora for strains producing metabolites with inhibitory effects on the human pathogenic oomycete Pythium insidiosum. Separation and characterization of extracts from Pseudomonas stutzeri with anti-Pythium inhibitory activity. Search for genes with anti-Pythium effect within the genome of P. stutzeri.
Methods:
A total of 88 bacterial strains were isolated from water resources in northeastern Thailand. Two screening methods were used to establish their inhibitory effects on P. insidiosum. One strain, P. stutzeri ST1302 was randomly chosen, and the extract with anti-P. insidiosum activity was fractionated and subfractionated using liquid column chromatography and purified by thin layer chromatography. The chemical structure of purified fractions was determined by Fourier transform infrared spectroscopy, nuclear magnetic resonance and mass spectrometry. Further, search for genes involved in the anti-Pythium activity (phenazine-1-carboxylic acid, 2,4-diacetylphloroglucinol, pyoluteorin and pyrrolnitrin) was undertaken in this P. stutzeri strain using primers described in the literature.
Results:
Anti-P. insidiosum activity was detected in 16 isolates (18.2%). In P. stutzeri ST1302, a subfraction labeled PYK7 exhibited strong activity against this oomycete. It was assigned to the diketopiperazines as cyclo(D-Pro-L-Val). In the search for genes, one gene region was successfully amplified. This corresponded to pyrrolnitrin. The results suggest the possibility of using the related metabolites against P. insidiosum. This is the first report on the inhibitory effects of P. stutzeri against this oomycete. The results may contribute to the development of antimicrobial drugs/probiotics against pythiosis.
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In this study, we investigated the effects of a change in growth temperature on the transcriptome of two strains of Pseudomonas aeruginosa. The chosen P. aeruginosa strains were M18 and PAO1, which are adapted to two different niches, rhizosphere and human, respectively. To assess the changes induced by a change in temperature, we used a newly designed microarray covering the complete genome of four P. aeruginosa strains: PAO1, M18, PA14 and LESB58, which proved informative and reliable for the transcriptome study. Using the microarray, we analysed the transcriptome profile changes of two P. aeruginosa strains of M18 and PAO1 at their originating and non-originating temperatures: 28 °C for the rhizosphere and 37 °C for the human. The transcriptome profiles showed significant temperature-dependent differences (64.8 % in M18 and 66.8 % in PAO1) compared with the genome structure (6 % in M18 and 4.1 % in PAO1). Furthermore, we found that the specific induced genes at the non-originating growth temperature of the each strain (207 genes in M18 and 229 genes in PAO1) were evidently more than those induced at the originating growth temperature (158 genes in M18 and 169 genes in PAO1). The functional analysis of several newly found specific regulated operons (such as phh, liu, hmg) in the two strains indicated possible strategies implemented to respond to the non-originating temperature. This study provides new insight into how P. aeruginosa species responds to temperature change and a microarray platform covering the complete genomes of four widely studied P. aeruginosa strains.
In Vitro Evaluation of Antagonistic Microorganisms for the Control of Die-Back of Neem Causal Agent Phomopsis Azadirachtae
The die-back of neem caused by Phomopsis azadirachtae is a devastating disease in India reducing the life span and seed production of neem. Six isolates of antagonistic bacteria and fungi, Bacillus cereus (MTCC 430), B. subtilis (MTCC 619), Pseudomonas aeruginosa (MTCC 2581), P. oleovorans (MTCC 617), Trichoderma harzianum (MTCC 792) and T. viride (MTCC 800) were evaluated against P. azadirachtae under in vitro conditions. Culture filtrates of all these microorganisms were extracted using ethyl acetate, and the obtained fractions were tested for their antifungal activity against P. azadirachtae at different concentrations. Ethyl acetate extracts of B. subtilis and P. aeruginosa were highly effective and completely inhibited the growth of P. azadirachtae at 25 ppm concentration. Both these isolates may be considered as factors for the biological control of die-back of neem.
Our previously published reports have described an effective biocontrol agent named Pseudomonas sp. M18 as its 16S rDNA sequence and several regulator genes share homologous sequences with those of P. aeruginosa, but there are several unusual phenotypic features. This study aims to explore its strain specific genomic features and gene expression patterns at different temperatures.
The complete M18 genome is composed of a single chromosome of 6,327,754 base pairs containing 5684 open reading frames. Seven genomic islands, including two novel prophages and five specific non-phage islands were identified besides the conserved P. aeruginosa core genome. Each prophage contains a putative chitinase coding gene, and the prophage II contains a capB gene encoding a putative cold stress protein. The non-phage genomic islands contain genes responsible for pyoluteorin biosynthesis, environmental substance degradation and type I and III restriction-modification systems. Compared with other P. aeruginosa strains, the fewest number (3) of insertion sequences and the most number (3) of clustered regularly interspaced short palindromic repeats in M18 genome may contribute to the relative genome stability. Although the M18 genome is most closely related to that of P. aeruginosa strain LESB58, the strain M18 is more susceptible to several antimicrobial agents and easier to be erased in a mouse acute lung infection model than the strain LESB58. The whole M18 transcriptomic analysis indicated that 10.6% of the expressed genes are temperature-dependent, with 22 genes up-regulated at 28°C in three non-phage genomic islands and one prophage but none at 37°C.
The P. aeruginosa strain M18 has evolved its specific genomic structures and temperature dependent expression patterns to meet the requirement of its fitness and competitiveness under selective pressures imposed on the strain in rhizosphere niche.
The highly diverse genus Pseudomonas contains very effective biocontrol agents that can increase plant growth and improve plant health. Biocontrol characteristics, however, are strain-dependent and cannot be clearly linked to phylogenetic variation. Isolate screening remains essential to find suitable strains, which can be done by testing large local collections for disease suppression and plant-growth promotion exemplified in a case study on forage legumes in Uruguay or by targeted screening for Pseudomonas spp. which produce desirable secondary metabolites, as demonstrated in a case study on cocoyam in Cameroon. In both case studies, access to reference strains from public and private collections was essential for identification, phylogenetic studies and metabolite characterization.
Molecular characterization of rhizobacterial isolate RM-3, based on sequencing of a partial 1,313-bp fragment of 16S rDNA amplicon, validated the strain as Pseudomonas aeruginosa. The strain showed significant growth inhibition of different phytopathogenic fungi in dual plate and liquid culture assays. Maximum growth inhibition was found in case of Macrophomina phaseolina in plate assay (68%), whereas it was 93% in Dreschlera graminae in dual liquid assay. Microscopic studies (light and scanning electron) showed morphological abnormalities such as perforation, fragmentation, swelling, shriveling and lysis of hyphae of pathogenic fungi. The strain also exhibited production of siderophore and hydrogen cyanide (HCN) on chrome azurol S and King's B media, respectively. Besides, this strain also produced extracellular chitinase enzyme and an important antibiotic, phenazine. Seed bacterization with RM-3 showed a significant (P < 0.05) increase in seed germination, shoot length, shoot fresh and dry weight, root length, root fresh and dry weight and leaf area. It was also able to colonize the rhizosphere of plants and reduced percent disease incidence in M. phaseolina-infested soil by 83%. Yield parameters such as pods, number of seeds and grain yield per plant also enhanced significantly (P < 0.05) in comparison to control. Thus, the secondary metabolites producing Pseudomonas aeruginosa strain RM-3 exhibited innate potential of plant growth promotion and biocontrol potential in vitro and in vivo.
ABSTRACT Application of salicylic acid induces systemic acquired resistance in tobacco. pchA and pchB, which encode for the biosynthesis of salicylic acid in Pseudomonas aeruginosa, were cloned into two expression vectors, and these constructs were introduced into two root-colonizing strains of P. fluorescens. Introduction of pchBA into strain P3, which does not produce salicylic acid, rendered this strain capable of salicylic acid production in vitro and significantly improved its ability to induce systemic resistance in tobacco against tobacco necrosis virus. Strain CHA0 is a well-described biocontrol agent that naturally produces salicylic acid under conditions of iron limitation. Introduction of pchBA into CHA0 increased the production of salicylic acid in vitro and in the rhizosphere of tobacco, but did not improve the ability of CHA0 to induce systemic resistance in tobacco. In addition, these genes did not improve significantly the capacity of strains P3 and CHA0 to suppress black root rot of tobacco in a gnotobiotic system.
ABSTRACT A 3-year experiment was conducted in field microplots infested with Fusarium oxysporum f. sp. ciceris race 5 at Córdoba, Spain, in order to assess efficacy of an integrated management strategy for Fusarium wilt of chickpea that combined the choice of sowing date, use of partially resistant chickpea genotypes, and seed and soil treatments with biocontrol agents Bacillus megaterium RGAF 51, B. subtilis GB03, nonpathogenic F. oxysporum Fo 90105, and Pseudomonas fluorescens RG 26. Advancing the sowing date from early spring to winter significantly delayed disease onset, reduced the final disease intensity (amount of disease in a microplot that combines disease incidence and severity, expressed as a percentage of the maximum possible amount of disease in that microplot), and increased chickpea seed yield. A significant linear relationship was found between disease development over time and weather variables at the experimental site, with epidemics developing earlier and faster as mean temperature increased and accumulated rainfall decreased. Under conditions highly conducive for Fusarium wilt development, the degree of disease control depended primarily on choice of sowing date, and to a lesser extent on level of resistance of chickpea genotypes to F. oxysporum f. sp. ciceris race 5, and the biocontrol treatments. The main effects of sowing date, partially resistant genotypes, and biocontrol agents were a reduction in the rate of epidemic development over time, a reduction of disease intensity, and an increase in chickpea seedling emergence, respectively. Chickpea seed yield was influenced by all three factors in the study. The increase in chickpea seed yield was the most consistent effect of the biocontrol agents. However, that effect was primarily influenced by sowing date, which also determined disease development. Effectiveness of biocontrol treatments in disease management was lowest in January sowings, which were least favorable for Fusarium wilt. Sowing in February, which was moderately favorable for wilt development, resulted in the greatest increase in seed yield by the biocontrol agents. In March sowings, which were most conducive for the disease, the biocontrol agents delayed disease onset and increased seedling emergence. B. subtilis GB03 and P. fluorescens RG 26, applied either alone or each in combination with nonpathogenic F. oxysporum Fo 90105, were the most effective treatments at suppressing Fusarium wilt, or delaying disease onset and increasing seed yield, respectively. The importance of integrating existing control practices, partially effective by themselves, with other control measures to achieve appropriate management of Fusarium wilt and increase of seed yield in chickpea in Mediterranean-type environments is demonstrated by the results of this study.
Tn5 mutagenesis of different fluorescent pseudomonads was achieved by conjugational transfer of the suicide vector pSUP 10141. Pyoverdine negative (Pvd-) mutants were detected by the absence of fluorescence on King's B medium and by their inability to grow in the presence of the iron chelator EDDHA [ethylenediamine di(o-hydroxyphenylacetic acid)]. In P. fluorescens ATCC 17400 and three rhizosphere isolates (one P. putida and two P. fluorescens), the percentage of Pvd- mutants ranged between 0 and 0.54%. In a P. chlororaphis rhizosphere isolate, this percentage was higher (4%). In these mutants both of the Tn5 antibiotic resistances (Km and Tc) were stable and the transposon could be detected by hybridization. In Pvd- mutants of P. fluorescens ATCC 17400, the transposon was found to be inserted twice in the chromosome while single insertions were detected in the DNA of other, randomly tested mutants. In P. aeruginosa PAO1, where 13.1% of the mutants were Pvd-, both antibiotic resistances were rapidly lost and accordingly no transposon insertion could be detected by hybridization. However, the Pvd- phenotype was generally stable in these mutants. The plasmid pNK862 containing a mini-Tn10 transposon was introduced by electroporation into P. aeruginosa PAO1 and Kmr mutants were recovered, 89% of which were Pvd- and confirmed to be P. aeruginosa by PCR amplification of the P. aeruginosa lipoprotein gene. The mini-Tn10 insertions were also found to be unstable in PAO1.
Certain members of the fluorescent pseudomonad group have been shown to be potential agents for the biocontrol of plant root diseases. The major problems with the commercialization of these beneficial strains are that few wild-type strains contain all the desired characteristics for this process and the performance of strains in different soil and climatic conditions is not reproducible. Consequently, prior to selection and/or improvement of suitable strains for biocontrol purposes, it is necessary to understand the important traits required for this purpose. The production of fluorescent siderophores (iron-binding compounds) and antibiotic compounds has been recognized as important for the inhibition of plant root pathogens. Efficient root colonization is also a prerequisite for successful biocontrol strains. This review discusses some of the characteristics of fluorescent pseudomonads that have been suggested to be important for biocontrol. The genetic organization and regulation of these processes is also examined. This information is necessary for attempts aimed at the improvement of strains based on deregulating pathways or introducing traits from one strain to another. The release of genetically engineered organisms into the environment is governed by regulations, and this aspect is summarized. The commercialization of fluorescent pseudomonads for the biological control of plant root diseases remains an exciting possibility. The understanding of the relevant characteristics will facilitate this process by enabling the direct selection and/or construction of strains which will perform under a variety of environmental conditions.
Phenazine antibiotics produced by Pseudomonas fluorescens 2-79 and Pseudomonas aureofaciens 30-84, previously shown to be the principal factors enabling these bacteria to suppress take-all of wheat caused by Gaeumannomyces graminis var. tritici, also contribute to the ecological competence of these strains in soil and in the rhizosphere of wheat. Strains 2-79 and 30-84, their Tn5 mutants defective in phenazine production (Phz-), or the mutant strains genetically restored for phenazine production (Phz+) were introduced into Thatuna silt loam (TSL) or TSL amended with G. graminis var. tritici. Soils were planted with three or five successive 20-day plant-harvest cycles of wheat. Population sizes of Phz- derivatives declined more rapidly than did population sizes of the corresponding parental or restored Phz+ strains. Antibiotic biosynthesis was particularly critical to survival of these strains during the fourth and fifth cycles of wheat in the presence of G. graminis var. tritici and during all five cycles of wheat in the absence of take-all. In pasteurized TSL, a Phz- derivative of strain 30-84 colonized the rhizosphere of wheat to the same extent that the parental strain did. The results indicate that production of phenazine antibiotics by strains 2-79 and 30-84 can contribute to the ecological competence of these strains and that the reduced survival of the Phz- strains is due to a diminished ability to compete with the resident microflora.
The mini Mu element Mu dII1681, which contains the lac operon genes and a kanamycin resistance gene, was inserted in the chromosome of plant growth-beneficial Pseudomonas aeruginosa 7NSK2 to construct a marked strain (MPB1). In MPB1, beta-galactosidase is permanently expressed under the culture conditions used. The MPB1 strain could be recovered with an efficiency of about 100% from a sandy loam soil on 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside medium containing sebacic acid and kanamycin. The limit of detection is about 10 CFU/g of soil. A detailed comparison was made between the wild-type strain 7NSK2 and the Mu dII1681-containing MPB1 strain. The results showed that no genes essential for growth, siderophore production, survival in sterile and nonsterile conditions, plant growth stimulation, or root colonization had been damaged in the MPB1 strain, which means that MPB1 can reliably be used for ecological studies in soil. MPB1 survived well at 4 or 28 degrees C but died off relatively rapidly in air-dried soil or at subzero temperatures. In these conditions, however, the MPB1 strain did not completely disappear from the soil but survived at a very low level of about 100 CFU/g of soil for more than 3 months. This observation stresses the need for very sensitive counting methods for ecological studies and for the evaluation of released microorganisms. Maize was inoculated with MPB1 via seed inoculation or soil inoculation. Upon seed inoculation, only the upper root parts were effectively colonized, while soil inoculation resulted in a complete colonization of the root system.
We show that the disease tomato foot and root rot caused by the pathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici can be controlled by inoculation of seeds with cells of the efficient root colonizer Pseudomonas fluorescens WCS365, indicating that strain WCS365 is a biocontrol strain. The mechanism for disease suppression most likely is induced systemic resistance. P. fluorescens strain WCS365 and P. chlororaphis strain PCL1391, which acts through the production of the antibiotic phenazine-1-carboxamide, were differentially labeled using genes encoding autofluorescent proteins. Inoculation of seeds with a 1:1 mixture of these strains showed that, at the upper part of the root, the two cell types were present as microcolonies of either one or both cell types. Microcolonies at the lower root part were predominantly of one cell type. Mixed inoculation tended to improve biocontrol in comparison with single inoculations. In contrast to what was observed previously for strain PCL1391, mutations in various colonization genes, including sss, did not consistently decrease the biocontrol ability of strain WCS365. Multiple copies of the sss colonization gene in WCS365 improved neither colonization nor biocontrol by this strain. However, introduction of the sss-containing DNA fragment into the poor colonizer P. fluorescens WCS307 and into the good colonizer P. fluorescens F113 increased the competitive tomato root tip colonization ability of the latter strains 16- to 40-fold and 8- to 16-fold, respectively. These results show that improvement of the colonization ability of wild-type Pseudomonas strains by genetic engineering is a realistic goal.
Rhizosphere colonization is one of the first steps in the pathogenesis of soilborne microorganisms. It can also be crucial for the action of microbial inoculants used as biofertilizers, biopesticides, phytostimulators, and bioremediators. Pseudomonas, one of the best root colonizers, is therefore used as a model root colonizer. This review focuses on (a) the temporal-spatial description of root-colonizing bacteria as visualized by confocal laser scanning microscopal analysis of autofluorescent microorganisms, and (b) bacterial genes and traits involved in root colonization. The results show a strong parallel between traits used for the colonization of roots and of animal tissues, indicating the general importance of such a study. Finally, we identify several noteworthy areas for future research.
The resurgence of interest in the use of introduced microorganisms for biological control of plant pathogens during the past 10 years has been driven in part by trends in agriculture toward greater sustainability and increased public concern for hazards associated with the use of synthetic pesticides. Rapidly evolving technologies from molecular biology and genetics have provided new insights into the underlying mechanisms by which biocontrol agents function and have allowed evaluation of the behavior of microbial inoculants in natural environments to a degree not previously possible. The results from these advances bear directly on two fundamental sources of inconsistency in the performance of microorganisms introduced for biological control that until now have retarded their commercial development and widespread use, namely, inadequate colonization of the target site and variability in the expression or level of activity of the mechanism(s) responsible for pathogen suppression.
Bacteria associated with the plant rhizosphere may have beneficial effects on plant growth by providing nutrients and growth factors, or by producing antibiotics and siderophores, which antagonize phytopathogenic fungi and bacteria. There is considerable experimental support for the idea that plant growth promoting bacteria may be used as bio–fertilizers or biological disease control agents to increase agricultural yields. Recent advances in our understanding of the molecular biology of the systems responsible for plant growth stimulation are opening the way to strain improvement by genetic engineering.
A total of 137 actinomycetes cultures, isolated from 25 different herbal vermicomposts, were characterized for their antagonistic potential against Fusarium oxysporum f. sp. ciceri (FOC) by dual-culture assay. Of the isolates, five most promising FOC antagonistic isolates (CAI-24, CAI-121, CAI-127, KAI-32 and KAI-90) were characterized for the production of siderophore, cellulase, protease, hydrocyanic acid (HCN), indole acetic acid (IAA) and antagonistic potential against Rhizoctonia bataticola, which causes dry root rot in chickpea (three strains viz. RB-6, RB-24 and RB-115) and sorghum (one strain). All of the five FOC antagonistic isolates produced siderophore and HCN, four of them (except KAI-90) produced IAA, KAI-32 and KAI-90 produced cellulase and CAI-24 and CAI-127 produced protease. In the dual-culture assay, three of the isolates, CAI-24, KAI-32 and KAI-90, also inhibited all three strains of R. bataticola in chickpea, while two of them (KAI-32 and KAI-90) inhibited the tested strain in sorghum. When the FOC antagonistic isolates were evaluated further for their antagonistic potential in the greenhouse and wilt-sick field conditions on chickpea, 45–76% and 4–19% reduction of disease incidence were observed, respectively compared to the control. The sequences of 16S rDNA gene of the isolates CAI-24, CAI-121, CAI-127, KAI-32 and KAI-90 were matched with Streptomyces tsusimaensis, Streptomyces caviscabies, Streptomyces setonii, Streptomyces africanus and an identified species of Streptomyces, respectively using the BLAST searching. This study indicated that the selected actinomycete isolates have the potential for biological control of Fusarium wilt disease in chickpea.
Study and comparison of efficiency of the antagonist species Trichoderma atroviride, T. harzianum and T. longibrachiatum against Fusarium wilt were carried out using in vitro and in vivo based bioassay. Significant decrease of both growth and conidia production of the pathogen are obtained compared to the control. Thus, the highest percentages of diameter colony reduction and conidial production were obtained with the T. atroviride isolate (Ta.13), causing 65.64% reduction in colony diameter (direct confrontation), 48.71% reduction in colony diameter (indirect confrontation), and a complete inhibition of conidial production. Once more in direct confrontation, T. atroviride overgrowth the pathogen colony and sporulate above. The seed treatment by Trichoderma spp. isolates before sowing in a soil already infested by the pathogen led to a significant decrease of disease severity compared to the untreated control. The weakest index of disease severity is obtained with the T. atroviride isolates (Ta.13), which cause 83.92% reduction compared to the control. The most effective isolates in protection chickpea seedlings against the disease were the three strains of T. atroviride species (Ta.3, Ta.7 and Ta.13) as well as the isolate T. harzianum (Th.16). Reduction of disease severity obtained was associated with an increase of the vegetal growth including the stem height as well as the plant fresh and dry weight.
Liddell, C. M., and Parke, J. L. 1989. Enhanced colonization of pea taproots by a fluorescent pseudomonad biocontrol agent by water infiltration into soil. Phytopathology 79:1327-1332. Root colonization by an introduced strain of Pseudomonasfluorescens bacterium could not be detected on roots beyond 3 cm from the seed, was examined to determine the importance of the root apex in passive more than 16 cm from the root apex. Addition of 27.2 and 54.4 mm transport and to quantify the effect of infiltrating water on distribution of water to the top of the columns 4 days after planting increased the of the bacterium. Pea seeds coated with strain PRA25rif of P.fluorescens depth from which PRA25rif was recovered. The bacterium was detected were sown in columns containing a sandy field soil at soil-water matric on root segments at least 9-10 cm from the seed 24 hr after water was potentials of -1, -6, or -10 kPa. After 7 days, the largest population applied. Transport of the bacterium on the root apex apparently was density of the bacterium was found on roots at -I kPa, but the bacterium limited to a short period after seed germination, but the bacterium was was detected on only 5% of root segments 4-5 cm below the seed, carried long distances by percolating water. approximately 8 cm above the root apex. At -6 and -10 kPa, the
Pseudomonas aeruginosa PNA1, isolated from the rhizosphere of chickpea in India, suppressed Fusarium wilt of chickpea, caused by Fusarium oxysporum f. sp. ciceris, and Pythium damping-off of bean, caused by Pythium splendens. When grown in culture, PNA1 produced the phenazine antibiotics phenazine-1-carboxylic acid and oxychloraphine, and inhibited mycelial growth of F. oxysporum f. sp. ciceris, P. splendens, and certain other phytopathogenic fungi. Two mutants (FM29 and FM13) deficient in phenazine production were obtained following transposon mutagenesis of PNA1. The transposon in the genome of FM29 was localized to phnA, which is thought to encode a subunit of anthranilate synthase II involved in the phenazine biosynthesis. The FM13 mutation was complemented by trpC, which encodes indole glycerol phosphate synthase in the tryptophan biosynthesis pathway; consequently, FM13 could not grow on a minimal medium in the absence of tryptophan. Neither FM29 nor FM13 suppressed Fusarium wilt of chickpea to the level achieved by the wild-type strain, indicating that phenazine production contributed to the biocontrol of this disease by P. aeruginosa PNA1. FM29 was also less effective than the phenazine-producing parental strain in biological control of Pythium damping-off of bean, but FM13 was as effective as the parental strain in suppressing this disease. Anthranilate, an intermediate in the tryptophan biosynthesis pathway, suppressed mycelial growth of Pythium spp. in culture and Pythium damping-off of bean and lettuce. Anthranilate, excreted by FM13 as a consequence of the trpC mutation, may have contributed to the suppression of Pythium damping-off by the mutant.
The effects of inoculum density (0, 4.6 × 107, 4.2 × 108, and 8.8 × 108 cfu∙mL−1), temperature (10, 20, and 30 °C), and plant genotype (cultivars Celebrity, Blazer, Scotia, and Mountain Delight) on bacterial colonization and plant growth promotion were investigated in a gnotobiotic system. An in vitro dual culture of tomato (Lycopersicon esculentum L.) plantlets and a Pseudomonas sp., strain PsJN, were used. Epiphytic (external) and endophytic (internal) bacterial populations were determined to evaluate plantlet colonization. Shoot and root biomass of bacterized plantlets was significantly higher (p ≤ 0.05) than that of nonbacterized controls. Growth promotion was best with inoculum densities of 3 × 108 – 7 × 108 cfu∙mL−1 at 20 °C, particularly in the early maturing cultivars Blazer and Scotia. Lower inoculum densities were required to maximize root growth (approximately 1 × 108 cfu∙mL−1) than shoot growth (approximately 3 × 108 cfu∙mL−1). Shoot surface populations did not vary with inoculum density or temperature, but the bacterium colonized the shoot exterior of cultivars Celebrity, Mountain Delight, and Scotia better than cultivar Blazer. The root surface populations increased linearly with increasing inoculum density (within a range of 107–108 cfu∙mL−1), decreased with increasing temperatures (from 10 to 30 °C), and were higher for the main season cultivar Celebrity than for cultivars Blazer, Scotia, and Mountain Delight. Populations of shoot endophytes did not vary with initial inoculum density or genotype but were affected by temperature; the highest colonization was at 10 °C. The number of root endophytes was also highest at 10 °C at the inoculum density of approximately 4 × 108 cfu∙mL−1 and did not vary with genotypes. The experiments clearly indicate that there was no relationship between root surface colonization and plant growth promotion. However, the range of inoculum levels (3 × 108 – 7 × 108 cfu∙mL−1) that promoted colonization of the inner root tissues (endophytic) also best promoted plant growth. A possible biostimulation threshold within the tissues of the inoculated plants under conditions favourable to the growth of tomato is proposed.Key words: Pseudomonas sp., tomato, colonization, growth promotion.
Seventy bacterial isolates from the rhizosphere of tomato were screened for antagonistic activity against the tomato foot and root rot-causing fungal pathogen Fusarium oxy-sporum f. sp. radicis-lycopersici. One isolate, strain PCL1391, appeared to be an efficient colonizer of tomato roots and an excellent biocontrol strain in an F. ox-ysporum/tomato test system. Strain PCL1391 was identi-fied as Pseudomonas chlororaphis and further characteri-zation showed that it produces a broad spectrum of antifungal factors (AFFs), including a hydrophobic com-pound, hydrogen cyanide, chitinase(s), and protease(s). Through mass spectrometry and nuclear magnetic reso-nance, the hydrophobic compound was identified as phenazine-1-carboxamide (PCN). We have studied the production and action of this AFF both in vitro and in vivo. Using a PCL1391 transposon mutant, with a lux re-porter gene inserted in the phenazine biosynthetic operon (phz), we showed that this phenazine biosynthetic mutant was substantially decreased in both in vitro antifungal ac-tivity and biocontrol activity. Moreover, with the same mu-tant it was shown that the phz biosynthetic operon is ex-pressed in the tomato rhizosphere. Comparison of the biocontrol activity of the PCN-producing strain PCL1391 with those of phenazine-1-carboxylic acid (PCA)-producing strains P. fluorescens 2-79 and P. aureofaciens 30-84 showed that the PCN-producing strain is able to suppress disease in the tomato/F. oxysporum system,
Endophytic Pseudomonas aeruginosa strain BP35 was originally isolated from black pepper grown in the rain forest in Kerala, India. Strain PaBP35 was shown to provide significant protection to black pepper against infections by Phytophthora capsici and Radopholus similis. For registration and implementation in disease management programmes, several traits of PaBP35 were investigated including its endophytic behaviour, biocontrol activity, phylogeny and toxicity to mammals. The results showed that PaBP35 efficiently colonized black pepper shoots and displayed a typical spatiotemporal pattern in its endophytic movement with concomitant suppression of Phytophthora rot. Confocal laser scanning microscopy revealed high populations of PaBP35::gfp2 inside tomato plantlets, supporting its endophytic behaviour in other plant species. Polyphasic approaches to genotype PaBP35, including BOX-PCR, recN sequence analysis, multilocus sequence typing and comparative genome hybridization analysis, revealed its uniqueness among P. aeruginosa strains representing clinical habitats. However, like other P. aeruginosa strains, PaBP35 exhibited resistance to antibiotics, grew at 25-41°C and produced rhamnolipids and phenazines. PaBP35 displayed strong type II secretion effectors-mediated cytotoxicity on mammalian A549 cells. Coupled with pathogenicity in a murine airway infection model, we conclude that this plant endophytic strain is as virulent as clinical P. aeruginosa strains. Safety issues related to the selection of plant endophytic bacteria for crop protection are discussed.
The potential of anthranilate in the control of Pythium-induced damping-off in horticultural crops was investigated under gnotobiotic conditions. Mutational studies of P. aeruginosa PNA1 led us to identify anthranilate as an antifungal compound active against Pythium species. Anthranilate inhibited growth of the Pythium species in vitro and a 50% growth inhibition was observed at the concentration of 30 μg/ml of anthranilate in GCY medium. The addition of anthranilate at 50 μg/g of potting mix protected lettuce, tomato and beans in vivo against Pythium-induced damping-off. In view of rapid germination of Pythium sporangia in response to seed or root exudates and followed by immediate infection, the use of anthranilate in the suppression of damping-off was investigated.
Pseudomonas aureofaciens are soil-borne root-colonizing bacteria that produce phenazine antibiotics. Populations of P. aureofaciens strain 30–84 increase over time on wheat roots in response to the presence of a specific fungal pathogen. Phenazine production is the primary mechanism responsible for the competitive fitness of P. aureofaciens in the rhizosphere. Analysis of phenazine gene (phz) expression demonstrates that phenazine biosynthesis in P. aureofaciens is regulated analogously to other bacterial genes involved in host-microbe interactions. Two genes, phzR and phzI, the products of which belong to the LuxR/LuxI family of cell density-dependent regulatory proteins, are required for phz expression. PhzR encodes a transcriptional activator that induces phz expression in response to the accumulation of a diffusible signal produced by PhzI. The requirement for phzI can be bypassed by exogenous diffusible signals produced by several other rhizosphere bacteria. We discuss phz regulation in the context of the ecology of P. aureofaciens on the plant root. We integrate both molecular and field observations to propose a model to explain these interactions between the plant, the pathogen and the bacterium. In addition, we discuss signaling among different bacterial populations in the rhizosphere and hypothesize that this signaling may influence phz expression and thus biological control by P. aureofaciens.
A procedure that consumes less screening time was developed for screening chickpea rhizosphere-competent bacteria for suppression
of the chickpea pathogenic fungi Fusarium oxysporum f. sp. ciceri, Rhizoctonia bataticola and Pythium sp. Of the 478 bacteria obtained by random selection of the predominant, morphologically distinct colonies, 386 strains that
effectively colonize chickpea roots could be divided broadly into three different groups. The first group consisted of 44
good chickpea rhizosphere colonizers with 107 to 108 colony-forming units (CFU)/g root; the second group consisted of 253 medium chickpea rhizosphere colonizers with 104 to 106 CFU/g root; and the third group consisted of 89 poor chickpea rhizosphere colonizers with 100 (nondetectable) to 103 CFU/g root. Forty-four Rifr strains from the first group of good chickpea rhizosphere colonizers were further screened for their in vitro biocontrol
activity against F. oxysporum f. sp. ciceri, R. bataticola, and Pythium sp. One bacterial strain was selected for further work because of its unique ability to inhibit all three fungi and its good
chickpea rhizosphere colonization ability. This is the first report of a single biocontrol bacterium active against three
most devastating pathogenic fungi of chickpea. In a greenhouse test, chickpea seed bacterization with P. fluorescens NBRI1303 increased the germination of seedlings by 25%, reduced the number of diseased plants by 45%, compared with nonbacterized
controls. Increases in seedling dry weight, shoot length, and root length ranged from 16% to 18%. Significant growth increases
in shoot length, dry weight, and grain yield, averaging 11.59%, 17.58%, and 22.61% respectively above untreated controls,
were attained in field trials in Agra and Jhansi. A rifampicin-resistant mutant P. fluorescens NBRI1303R of the P. fluorescens NBRI1303, used to monitor chickpea root colonization, confirmed the rapid and aggressive colonization by the bacterium, making
it a potential biocontrol agent against chickpea phytopathogenic fungi. The results, demonstrating an increase in the efficiency
of screening and detection of plant beneficial strains, should greatly benefit future studies.
The species of bacteria associated with rhizosphere and roots of maize exhibited varying degrees of antagonism towards Fusarium moniliforme, which was dependent upon the soils from which the bacteria were isolated. Pseudomonas fluorescens, P. putida, P. cepacia, Flavobacterium/CDC group II, Enterobacter cloacae, E. agglomerons, Acinetobacter calcoaceticus. Bacillus spp, and various actinomycetes were the antagonistic bacteria most frequently isolated from maize-growing soils. In vitro inhibition depended on the agar medium used and also on the age of the bacterial culture. Bacteria belonging to the group Pseudomonas such as P. fluorescens, P. putida and P. cepacia, which formed 88% of the antagonistic Gram-negative bacteria isolated were more inhibitory to F. moniliforme than the other antagonists and were isolated in high numbers from both maize seedlings and mature plants. Isolation of antagonists from surface sterilized roots indicate their close association with maize roots. Antibiotic production rather than siderophores seem to be responsible for the antifungal activity of antagonistic bacteria.
Over 13 500 chickpea (Cicer arietinum L.) germplasm accessions from 40 countries were evaluated for resistance to race 1 of Fusarium oxysporum f.sp. ciceri at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), Patancheru, India. One hundred and sixty accessions were found resistant through field and pot screenings. Many of these resistant accessions originated from India and Iran. One hundred and fifty wilt-resistant lines were desi types as against ten kabuli types.
Sunflower necrosis virus disease (SNVD) was reported to cause a significant damage to sunflower production in India. Based on the biocontrol efficacy against SNVD observed in the previous greenhouse experiments, two plant growth promoting microbial consortia (PGPMCs) viz., PGPMC-1 consisting of Bacillus licheniformis strain MML2501 + Bacillus sp. strain MML2551 + Pseudomonas aeruginosa strain MML2212 + Streptomyces fradiae strain MML1042 and PGPMC-2 consisting of B. licheniformis MML2501 + Bacillus sp. MML2551 + P. aeruginosa MML2212 were used in the present study. Powder and liquid formulations of the above plant growth promoting microorganisms (PGPMs) were evaluated along with farmers' practice (imidacloprid + mancozeb) and control in farmers' fields. Significant disease reduction, increase of seed germination, plant height and yield parameters with an additional seed yield of 840 kg/ha, an additional income of Rs. 10,920/ha and benefit cost ratio of 6.1 were recorded following treatment with a powder formulation of PGPMC-1 compared to control. Further, liquid formulation of PGPMC-1 significantly reduced SNVD up to 51.4% compared to control. Besides, this treatment improved the seed germination (24.4%), plant height (61.3%), yield parameters with an additional seed yield of 936 kg/ha and an additional income of Rs. 12,168/ha. Benefit cost ratio was calculated as 6.8 in this treatment compared to 4.6 and 3.7, respectively for PGPMC-2 liquid formulation and farmers' practice compared to control. This is the first report of PGPMCs mediated biological control of SNVD under field conditions.
Antagonistic fluorescent pseudomonads isolated from rice rhizospheric soil were characterized using biochemical, taxonomical and molecular tools. Production of cyclopropane fatty acid (CFA) was correlated with their antagonistic potential. Strains were grouped into 18 different genotypes on the basis of amplified ribosomal DNA restriction analysis (ARDRA) and repetitive (rep)-PCR based genotypic fingerprinting analyses. High phylogenetic resolution among antagonistic fluorescent pseudomonad strains was obtained based on the DNA gyrase B subunit (gyrB) and RNA polymerase sigma factor 70 (rpoD) gene sequence analyses. Combined gyrB and rpoD sequence analysis resulted in the accurate estimation of molecular phylogeny and provided a significant correlation between the genetic distances among strains. Present study demonstrated the genetic and functional relationship of fluorescent pseudomonads. The knowledge on genetic and functional potential of fluorescent pseudomonads associated with rice rhizosphere is useful to understand their ecological role and for their utilization in sustainable agriculture.
Streptomyces scabies causes common scab, an economical disease affecting potato crops world-wide, for which no effective control measure exists. This pathogen produces the plant toxin thaxtomin A, which is involved in symptom development on potato tubers. A biological control approach that can limit S. scabies growth and repress thaxtomin production represents an attractive alternative to classical control strategies. Pseudomonas sp. LBUM 223 produces phenazine-1-carboxylic acid (PCA), an antibiotic that inhibits the growth of plant pathogens and contributes to the biological control of plant diseases. In this study, the involvement of LBUM 223's PCA-producing ability in the growth inhibition of S. scabies, repression of thaxtomin biosynthesis genes (txtA and txtC) and the biological control of common scab of potato was investigated using a mutant defective in PCA production (LBUM 223phzC(-) ). Streptomyces scabies growth was inhibited to a significantly lesser degree by LBUM 223phzC(-) than by the wild type. LBUM 223 also significantly repressed txtA and txtC expression in S. scabies and protected potato against disease, whereas LBUM 223phzC(-) did not. These results suggest that PCA production is central to the ability of LBUM 223 to limit pathogen growth, repress the expression of key pathogenicity genes and control common scab of potato.
ABSTRACT Bacillus sp. L324-92 is suppressive to three root diseases of wheat, namely take-all caused by Gaeumannomyces graminis var. tritici, Rhizoctonia root rot caused by Rhizoctonia solani AG8, and Pythium root rot caused by several Pythium species. Populations of strain L324-92R(12), a rifampicin-resistant mutant of L324-92 applied as a seed treatment, were monitored in the rhizosphere and spermosphere of wheat and compared with populations of Pseudomonas fluorescens 2-79RN(10), a known, rhizosphere-competent, biocontrol agent. In growth chamber studies, the population sizes of L324-92R(12) on roots of wheat were approximately 1,000-fold smaller than those of 2-79RN(10) at 5 days after planting, but, thereafter, they increased while those of 2-79RN(10) decreased until the two were equal in size at 45 days after planting. In the field with winter wheat, the population sizes of L324-92R(12) on roots were at least 10-fold smaller than those of 2-79RN(10) during the fall (November 1993) and early spring (March 1994). Thereafter, the population of L324-92R(12) remained constant or increased slightly, while the population of 2-79RN(10) decreased until the two were roughly the same at 10(4) to 10(5) CFU/plant over the period of 150 days (April 1994) until 285 days (harvest) after planting. In growth chamber studies, strain L324-92R(12) remained confined to root sections within 3.5 cm below the seed, whereas 2-79RN(10) was recovered from all root sections ranging from 0.5 to 6.5 cm below the seed. In the field on winter wheat, both strains were recovered from root sections down to 5.0 to 6.5 cm below the seed at 75 days after planting (mid December), but only 2-79RN(10) was recovered at this depth at 90 days after planting. Both strains were recovered from the seed remnants 6 months after planting in the field. Both strains also were recovered from inside the roots and shoots, but population sizes of strain 279RN(10) were greater than those of L324 92R(12).
Pseudomonas aureofaciens strain 30-84 suppresses take-all disease of wheat caused by Gaeumannomyces graminis var. tritici. Three antibiotics, phenazine-1-carboxylic acid, 2-hydroxyphenazine-1-carboxylic acid, and 2-hydroxyphenazine, were responsible for disease suppression. Tn5-induced mutants deficient in production of one or more of the antibiotics (Phz-) were significantly less suppressive than the parental strain. Cosmids pLSP259 and pLSP282 from a genomic library of strain 30-84 restored phenazine production and fungal inhibition to 10 different Phz- mutants. Sequences required for production of the phenazines were localized to a segment of approximately 2.8 kilobases that was present in both cosmids. Expression of this locus in Escherichia coli required the introduction of a functional promoter, was orientation-specific, and resulted in the production of all three phenazine antibiotics. These results strongly suggest that the cloned sequences encode a major portion of the phenazine biosynthetic pathway.
A collection of Tn5-derived minitransposons has been constructed that simplifies substantially the generation of insertion mutants, in vivo fusions with reporter genes, and the introduction of foreign DNA fragments into the chromosome of a variety of gram-negative bacteria, including the enteric bacteria and typical soil bacteria like Pseudomonas species. The minitransposons consist of genes specifying resistance to kanamycin, chloramphenicol, streptomycin-spectinomycin, and tetracycline as selection markers and a unique NotI cloning site flanked by 19-base-pair terminal repeat sequences of Tn5. Further derivatives also contain lacZ, phoA, luxAB, or xylE genes devoid of their native promoters located next to the terminal repeats in an orientation that affords the generation of gene-operon fusions. The transposons are located on a R6K-based suicide delivery plasmid that provides the IS50R transposase tnp gene in cis but external to the mobile element and whose conjugal transfer to recipients is mediated by RP4 mobilization functions in the donor.
Pseudomonas fluorescens 2-79 (NRRL B-15132) and its rifampin-resistant derivative 2-79RN10 are suppressive to take-all, a major root disease of wheat caused by Gaeumannomyces graminis var. tritici. Strain 2-79 produces the antibiotic phenazine-1-carboxylate, which is active in vitro against G. graminis var. tritici and other fungal root pathogens. Mutants defective in phenazine synthesis (Phz-) were generated by Tn5 insertion and then compared with the parental strain to determine the importance of the antibiotic in take-all suppression on wheat roots. Six independent, prototrophic Phz- mutants were noninhibitory to G. graminis var. tritici in vitro and provided significantly less control of take-all than strain 2-79 on wheat seedlings. Antibiotic synthesis, fungal inhibition in vitro, and suppression of take-all on wheat were coordinately restored in two mutants complemented with cloned DNA from a 2-79 genomic library. These mutants contained Tn5 insertions in adjacent EcoRI fragments in the 2-79 genome, and the restriction maps of the region flanking the insertions and the complementary DNA were colinear. These results indicate that sequences required for phenazine production were present in the cloned DNA and support the importance of the phenazine antibiotic in disease suppression in the rhizosphere.
Plant-growth-promoting rhizobacteria (PGPRs) are used as inoculants for biofertilization, phytostimulation and biocontrol. The interactions of PGPRs with their biotic environment, for example with plants and microorganisms, are often complex. Substantial advances in elucidating the genetic basis of the beneficial effects of PGPRs on plants have been made, some from whole-genome sequencing projects. This progress will lead to a more efficient use of these strains and possibly to their improvement by genetic modification.